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.