[media] tm6000: check an allocation for failure

This allocation had no error checking.  It didn't need to be under
the mutex so I moved it out form there. That makes the error handling
easier and is a potential speed up.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>