media: atomisp: make array idx_map static const

Don't populate the array idx_map on the stack but instead make it
static const. Also makes the object code smaller by 16 bytes.

Link: https://lore.kernel.org/linux-media/20211129230626.549090-1-colin.i.king@gmail.com


Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>