media: atomisp: Remove 1 line atomisp_flush_bufs_and_wakeup() helper

After recent changes this now is just a wrapper around
atomisp_flush_video_pipe(). Make its single caller call
atomisp_flush_video_pipe() directly and drop the helper.

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>