Bluetooth: btrtl: Prevent potential NULL dereference

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

Bluetooth: btrtl: Prevent potential NULL dereference

The btrtl_initialize() function checks that rtl_load_file() either

had an error or it loaded a zero length file. However, if it loaded

a zero length file then the error code is not set correctly. It

results in an error pointer vs NULL bug, followed by a NULL pointer

dereference. This was detected by Smatch:

drivers/bluetooth/btrtl.c:592 btrtl_initialize() warn: passing zero to 'ERR_PTR'