drivers/rtc/rtc-m41t80.c: propagate error value from smbus functions

Don't replace the value we got from the I2C layer, just pass it on.

Signed-off-by: Wolfram Sang <wsa@sang-engineering.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>