phy: qcom-qmp-combo: rename DP_PHY register pointer

The DP_PHY registers have erroneously been referred to as "PCS"
registers since DisplayPort support was added to the QMP drivers
(including in the devicetree binding).

Rename the corresponding pointer to match the register names.

Note that the repeated "dp" in the field name is intentional and this DP
register block is called "DP_PHY" (not just "PHY").
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20221121085058.31213-13-johan+linaro@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>