clk: qcom: gdsc: treat optional supplies as optional

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>

drivers/clk/qcom/gdsc.c

@@ -487,9 +487,14 @@ int gdsc_register(struct gdsc_desc *desc,
 		if (!scs[i] || !scs[i]->supply)
 			continue;
 
-		scs[i]->rsupply = devm_regulator_get(dev, scs[i]->supply);
-		if (IS_ERR(scs[i]->rsupply))
-			return PTR_ERR(scs[i]->rsupply);
+		scs[i]->rsupply = devm_regulator_get_optional(dev, scs[i]->supply);
+		if (IS_ERR(scs[i]->rsupply)) {
+			ret = PTR_ERR(scs[i]->rsupply);
+			if (ret != -ENODEV)
+				return ret;
+
+			scs[i]->rsupply = NULL;
+		}
 	}
 
 	data->num_domains = num;