media: atomisp: Remove __atomisp_get_pipe() helper

Remove the complicated __atomisp_get_pipe() helper, atomisp_buf_done()
only needs the pipe pointer in cases where it has a frame, so we can
simply get the pipe from the frame using the vb_to_pipe() helper.

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