phy: cadence: Sierra: remove redundant initialization of pointer regmap

The pointer regmap is being initialized with a value that is never
read and it is being updated later with a new value from
phy->regmap_common_cdb.  The initialization is redundant and can be
removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>