V4L/DVB (12200): mt312: Fix checkpatch warnings

This patch fixes some checkpatch warnings in mt312-driver.

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>