HID: check empty report_list in bigben_probe()

Add a check for empty report_list in bigben_probe().
The missing check causes a type confusion when issuing a list_entry()
on an empty report_list.
The problem is caused by the assumption that the device must
have valid report_list. While this will be true for all normal HID
devices, a suitably malicious device can violate the assumption.

Fixes: 256a90ed

 ("HID: hid-bigbenff: driver for BigBen Interactive PS3OFMINIPAD gamepad")
Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>