media: atomisp: remove the repeated declaration

Function 'ia_css_mmu_invalidate_cache' is declared twice, remove the
repeated declaration.

Link: https://lore.kernel.org/linux-media/1621922559-1859-1-git-send-email-zhangshaokun@hisilicon.com


Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>