Since commit deebc79b ("clk: qcom: gpucc-sc8280xp: Add external
supply for GX gdsc") the GDSC supply must be treated as optional to
avoid warnings like:

	gpu_cc-sc8280xp 3d90000.clock-controller: supply vdd-gfx not found, using dummy regulator

on SC8280XP.

Fortunately, the driver is already prepared to handle this by checking
that the regulator pointer is non-NULL before use.

This also avoids triggering a potential deadlock on SC8280XP even if the
underlying issue still remains for the derivative platforms like SA8295P
that actually use the supply.

Fixes: deebc79b ("clk: qcom: gpucc-sc8280xp: Add external supply for GX gdsc")
Link: https://lore.kernel.org/lkml/Zf25Sv2x9WaCFuIH@hovoldconsulting.com/Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20240325085835.26158-1-johan+linaro@kernel.orgSigned-off-by: Bjorn Andersson <andersson@kernel.org>