phy: usb: sunplus: Fix potential null-ptr-deref in sp_usb_phy_probe()

In the Linux kernel, the following vulnerability has been resolved: phy: usb: sunplus: Fix potential null-ptr-deref in sp_usb_phy_probe() sp_usb_phy_probe() will call platform_get_resource_byname() that may fail and return NULL. devm_ioremap() will use usbphy->moon4_res_mem->start as input, which may causes null-ptr-deref. Check the ret value of platform_get_resource_byname() to avoid the null-ptr-deref.