rtlwifi: use s8 instead of char

Compiling the rtlwifi drivers for ARM with gcc -Wextra warns about lots of
incorrect code that results from 'char' being unsigned here, e.g.

realtek/rtlwifi/rc.c:113:18: error: comparison is always true due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8188ee/dm.c:1070:22: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8192ce/trx.c:54:16: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8192cu/mac.c:601:16: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8192de/trx.c:53:16: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8192ee/phy.c:1268:12: error: comparison is always true due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8192se/rf.c:150:20: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8723be/dm.c:877:29: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8723be/phy.c:386:16: error: comparison is always true due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8821ae/dm.c:1514:38: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8821ae/phy.c:1558:11: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8821ae/phy.c:386:24: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/rtl8821ae/trx.c:55:12: error: comparison is always false due to limited range of data type [-Werror=type-limits]
realtek/rtlwifi/stats.c:31:16: error: comparison is always false due to limited range of data type [-Werror=type-limits]

This patch changes all uses of 'char' in this driver that refer to
8-bit integers to use 's8' instead, which is signed on all architectures.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/mac.c b/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/mac.c
index 0357133..68ca734 100644
--- a/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/mac.c
+++ b/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/mac.c
@@ -596,7 +596,7 @@
 
 /*==============================================================*/
 
-static u8 _rtl92c_query_rxpwrpercentage(char antpower)
+static u8 _rtl92c_query_rxpwrpercentage(s8 antpower)
 {
 	if ((antpower <= -100) || (antpower >= 20))
 		return 0;
@@ -606,9 +606,9 @@
 		return 100 + antpower;
 }
 
-static u8 _rtl92c_evm_db_to_percentage(char value)
+static u8 _rtl92c_evm_db_to_percentage(s8 value)
 {
-	char ret_val;
+	s8 ret_val;
 
 	ret_val = value;
 	if (ret_val >= 0)