[media] davinci: vpfe: fix error path in probe

The error path on failure was calling mutex_unlock(), but there was
no actuall call before for mutex_lock(). This patch fixes this issue
by pointing it to proper go label.

Reported-by: Jose Pablo Carballo <jose.carballo@ridgerun.com>
Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>