media: mt312: fix a missing check of mt312 reset

mt312_reset() may fail. Although it is called in the end of
mt312_set_frontend(), we better check its status and return its error
code upstream instead of 0.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Reviewed-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>