atomisp_get_metadata_type() always returns ATOMISP_MAIN_METADATA,
replace its uses with ATOMISP_MAIN_METADATA and remove it.

Link: https://lore.kernel.org/r/20230221145906.8113-7-hdegoede@redhat.comReviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>