rtc: ds1302: remove redundant initializations of pointer bp

Pointe bp is being initialized and this value is never read, it
is being updated to the same value later just before it is going to
be used. Remove the initialization as it is never read and keep
the setting of bp closer to the use of bp.

Cleans up clang warnings:
drivers/rtc/rtc-ds1302.c:115:7: warning: Value stored to 'bp' during
its initialization is never read
drivers/rtc/rtc-ds1302.c:46:7: warning: Value stored to 'bp' during
its initialization is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>