[media] dibusb: fix possible memory leak in dibusb_rc_query()

'buf' is malloced in dibusb_rc_query() and should be freed before
leaving from the error handling cases, otherwise it will cause
memory leak.

Fixes: ff1c1235

 ("[media] dibusb: handle error code on RC query")

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>