media: atomisp: Remove redundant NULL check

Fix warnings reported by coccicheck:
./drivers/staging/media/atomisp/pci/runtime/isp_param/src/isp_param.c:159:4-10: WARNING: NULL check before some freeing functions is not needed.

Link: https://lore.kernel.org/linux-media/20201225083818.64588-1-vulab@iscas.ac.cn


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