phy: cadence: Sierra: Rename some regmap variables to be in sync with Sierra documentation

No functional change. Rename some regmap variables as mentioned in Sierra
register description documentation.

Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
Reviewed-by: Aswath Govindraju <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20211223060137.9252-7-sjakhade@cadence.com


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