Bluetooth: btrtl: Prevent potential NULL dereference

[ Upstream commit 324dddea321078a6eeb535c2bff5257be74c9799 ]

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'

Fixes: 26503ad2 ("Bluetooth: btrtl: split the device initialization into smaller parts")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>