HID: bigbenff: prevent null pointer dereference

When emulating the device through uhid, there is a chance we don't have
output reports and so report_field is null.

Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20211202095334.14399-3-benjamin.tissoires@redhat.com

drivers/hid/hid-bigbenff.c

@@ -191,7 +191,7 @@ static void bigben_worker(struct work_struct *work)
 		struct bigben_device, worker);
 	struct hid_field *report_field = bigben->report->field[0];
 
-	if (bigben->removed)
+	if (bigben->removed || !report_field)
 		return;
 
 	if (bigben->work_led) {