[media] atomisp: don't treat warnings as errors

Several atomisp files use:
	 ccflags-y += -Werror

As, on media, our usual procedure is to use W=1, and atomisp
has *a lot* of warnings with such flag enabled,like:

./drivers/staging/media/atomisp/pci/atomisp2/css2400/hive_isp_css_common/host/system_local.h:62:26: warning: 'DDR_BASE' defined but not used [-Wunused-const-variable=]

At the end, it causes our build to fail, impacting our workflow.

So, remove this crap. If one wants to force -Werror, he
can still build with it enabled by passing a parameter to
make.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>