CVE-2021-47279 usb: misc: brcmstb-usb-pinmap: check return value after calling platform_get_resource()

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

usb: misc: brcmstb-usb-pinmap: check return value after calling platform_get_resource()

It will cause null-ptr-deref if platform_get_resource() returns NULL,
we need check the return value.