media: atomisp: Remove unneeded null check

In ia_css_frame_map, the check of 'err' is unneeded to be done twice.

Link: https://lore.kernel.org/linux-media/20211110094910.67951-1-vulab@iscas.ac.cn


Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>