i2c: Bus drivers return -Errno not -1

Tighten error paths used by various i2c adapters (mostly x86) so
they return real fault/errno codes instead of a "-1" (which is
most often interpreted as "-EPERM").  Build tested, with eyeball
review.

One minor initial goal is to have adapters consistently return
the code "-ENXIO" when addressing a device doesn't get an ACK
response, at least in the probe paths where they are already
good at stifling related logspam.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
diff --git a/drivers/i2c/busses/i2c-amd756-s4882.c b/drivers/i2c/busses/i2c-amd756-s4882.c
index c38a0a1..2f150e3 100644
--- a/drivers/i2c/busses/i2c-amd756-s4882.c
+++ b/drivers/i2c/busses/i2c-amd756-s4882.c
@@ -58,7 +58,7 @@
 	/* We exclude the multiplexed addresses */
 	if (addr == 0x4c || (addr & 0xfc) == 0x50 || (addr & 0xfc) == 0x30
 	 || addr == 0x18)
-		return -1;
+		return -ENXIO;
 
 	mutex_lock(&amd756_lock);
 
@@ -86,7 +86,7 @@
 
 	/* We exclude the non-multiplexed addresses */
 	if (addr != 0x4c && (addr & 0xfc) != 0x50 && (addr & 0xfc) != 0x30)
-		return -1;
+		return -ENXIO;
 
 	mutex_lock(&amd756_lock);