[media] staging: css2400/Makefile: don't include non-existing files

The atomisp css2400/Makefile includes a Makefile.common:

	include $(srctree)/$(src)/../Makefile.common

Well, this file doesn't exist at the Kernel tree :-)

So, don't include it.

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