V4L/DVB: davinci: don't return under lock on error path

If the kmalloc() failed for "ccdc_cfg = kmalloc(...);" then we would exit
with the lock held.  I moved the mutex_lock() below the allocation
because it isn't protecting anything in that block and allocations are
allocations are sometimes slow.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>