phy: cadence: Sierra: Remove unused `regmap` field from state struct

The driver state struct for the sierra PHY driver has a field named
`regmap` that is never referenced. Remove it since it is unused.

Not that there are separate fields of type `struct regmap` for the
individual sections of the device's register map. These other regmaps are
used and not affected by the patch.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20220707071722.44201-1-lars@metafoo.de


Signed-off-by: Vinod Koul <vkoul@kernel.org>