rtc: v3020: remove redundant initialization of variable retval

The variable retval is being initialized with a value that is never read,
it is being updated later on. The assignment is redundant and can be
removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210609120050.185746-1-colin.king@canonical.com