phy: qcom-qmp-combo: fix NULL-deref on runtime resume

Commit fc646236 ("phy: qcom-qmp-combo,usb: add support for separate
PCS_USB region") started treating the PCS_USB registers as potentially
separate from the PCS registers but used the wrong base when no PCS_USB
offset has been provided.

Fix the PCS_USB base used at runtime resume to prevent dereferencing a
NULL pointer on platforms that do not provide a PCS_USB offset (e.g.
SC7180).

Fixes: fc646236

 ("phy: qcom-qmp-combo,usb: add support for separate PCS_USB region")
Cc: stable@vger.kernel.org	# 5.20
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/20221026162116.26462-1-johan+linaro@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>