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

In the Linux kernel, the following vulnerability has been resolved: 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.