[media] cobalt: fix copy-and-paste error

The vmr_stat variable was filled with the contents of the control register,
not the status register. Classic copy-and-paste error.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>