rtc: m41t80: Complete error propagation from SMBus calls

Complement commit 85d77047

 ("drivers/rtc/rtc-m41t80.c: propagate
error value from smbus functions") and correct the remaining places that
fail to propagate the error code from SMBus calls.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
References: 85d77047

 ("drivers/rtc/rtc-m41t80.c: propagate error value from smbus functions")
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>