media: atomisp: Simplify atomisp_open() and atomisp_release()

Now that continuous mode is gone and we only have 1 /dev/video# node,
combined with only allowing 1 open of that /dev/video# node for now,
there is no need to check for other (sub)dev / pipe users.

Remove the unnecessary checks for a nice cleanup.

Note we also don't need to set asd->streaming to disabled since
the vb2_fop_release() call done by atomisp_release() will have called
atomisp_stop_streaming() already at this point (if necessary) and
that will have already done this.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>