ath: Make ath_printk void not int and remove unused struct ath_common *

Changing the return type and removing the unused argument from
ath_printk reduces code size.

Add an __always_unused struct ath_common * to the macros
that call ath_printk to avoid unused variable warnings.

$ size drivers/net/wireless/ath/built-in.o*
   text	   data	    bss	    dec	    hex	filename
1159859	  16235	 212000	1388094	 152e3e	drivers/net/wireless/ath/built-in.o.new
1164175	  16235	 212032	1392442	 153f3a	drivers/net/wireless/ath/built-in.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/main.c b/drivers/net/wireless/ath/main.c
index c325202..d9218fe 100644
--- a/drivers/net/wireless/ath/main.c
+++ b/drivers/net/wireless/ath/main.c
@@ -57,22 +57,18 @@
 }
 EXPORT_SYMBOL(ath_rxbuf_alloc);
 
-int ath_printk(const char *level, struct ath_common *common,
-	       const char *fmt, ...)
+void ath_printk(const char *level, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
-	int rtn;
 
 	va_start(args, fmt);
 
 	vaf.fmt = fmt;
 	vaf.va = &args;
 
-	rtn = printk("%sath: %pV", level, &vaf);
+	printk("%sath: %pV", level, &vaf);
 
 	va_end(args);
-
-	return rtn;
 }
 EXPORT_SYMBOL(ath_printk);