V4L/DVB (8917): saa7134-empress: fix changing the capture standard for non-tuner inputs

When changing the standard the saa6752hs was not updated unless the input
was the TV tuner. The saa6752hs should be updated regardless of the input.

In addition the S_STD and G_STD ioctls for the mpeg video device didn't do
anything. This is now fixed: they behave just like S_STD and G_STD on the
video0 device.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>