media: atomisp: make array idx_map static const

Don't populate the read-only array idx_map on the stack but
instead it static const. Also makes the object code a little smaller.

Link: https://lore.kernel.org/linux-media/20220109195129.46118-1-colin.i.king@gmail.com



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