drivers: flash: Do not unlock CR at the end of initialization

Unlocking CR at the end of initialization was added in commit
a9183cd5. It was probably copied
from previous flash driver implementation.

Unlocking and locking CR in write and erase functions was added in
commit 6e4cdb0c. Since we always unlock
the register before writing or erasing, and lock it after the operation
is finished, there is no need to unlock it after initialization.

Signed-off-by: Patryk Duda <pdk@semihalf.com>