media: em28xx: fix memory leak

If some error occurs, URB buffers should also be freed. If they aren't
freed with the dvb here, the em28xx_dvb_fini call doesn't frees the URB
buffers as dvb is set to NULL. The function in which error occurs should
do all the cleanup for the allocations it had done.

Tested the patch with the reproducer provided by syzbot. This patch
fixes the memleak.

Reported-by:  <syzbot+889397c820fa56adf25d@syzkaller.appspotmail.com>
Signed-off-by: Muhammad Usama Anjum <musamaanjum@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>