phy: qcom-qmp-pcie-msm8996: clean up power-down handling

phy: qcom-qmp-pcie-msm8996: clean up power-down handling

This driver uses v2 registers only so drop the unnecessary
POWER_DOWN_CONTROL override.

Note that this register is already hard-coded when powering on the PHY.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20221017065013.19647-7-johan+linaro@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>