media: staging: atomisp: get rid of an unused var

As warned:
	drivers/staging/media/atomisp/pci/atomisp2/css2400/sh_css.c:8085 create_host_regular_capture_pipeline() error: uninitialized symbol 'frm'.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>