V4L/DVB (13321): radio-gemtek-pci: fix double mutex_lock

Double mutexlock found by the Linux Driver Verification project and
reported by Alexander Strakh.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
CC: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>