phy: qcom-qmp-usb: Fix an NULL vs IS_ERR() bug

The qmp_usb_iomap() helper function currently returns the raw result of
devm_ioremap() for non-exclusive mappings. Since devm_ioremap() may return
a NULL pointer and the caller only checks error pointers with IS_ERR(),
NULL could bypass the check and lead to an invalid dereference.

Fix the issue by checking if devm_ioremap() returns NULL. When it does,
qmp_usb_iomap() now returns an error pointer via IOMEM_ERR_PTR(-ENOMEM),
ensuring safe and consistent error handling.

Signed-off-by: Chenyuan Yang <[e-mail]>
Fixes: a5d6b1ac56cb ("phy: qcom-qmp-usb: fix memleak on probe deferral")
CC: Johan Hovold <[e-mail]>
CC: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Johan Hovold <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/phy/qualcomm/phy-qcom-qmp-usb.c

···
 					int index, bool exclusive)
 {
 	struct resource res;
+	void __iomem *mem;
 
 	if (!exclusive) {
 		if (of_address_to_resource(np, index, &res))
 			return IOMEM_ERR_PTR(-EINVAL);
 
-		return devm_ioremap(dev, res.start, resource_size(&res));
+		mem = devm_ioremap(dev, res.start, resource_size(&res));
+		if (!mem)
+			return IOMEM_ERR_PTR(-ENOMEM);
+		return mem;
 	}
 
 	return devm_of_iomap(dev, np, index, NULL);