rtc: class: remove redundant assignment to variable err

rtc: class: remove redundant assignment to variable err

The variable err is being initialized with a value that is never read
and it is being updated later with a new value. The initialization
is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20200402110411.508534-1-colin.king@canonical.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>