[media] staging: media: atomisp: fix non static symbol warnings

Fix a couple of sparse warnings:
drivers/staging/media/atomisp/pci/atomisp2/atomisp_v4l2.c:59:14: warning: symbol 'repool_pgnr' was not declared. Should it be static?
drivers/staging/media/atomisp/pci/atomisp2/atomisp_v4l2.c:387:6: warning: symbol 'punit_ddr_dvfs_enable' was not declared. Should it be static?

Mark these symbols as static, so they are no longer incorrectly exported.

Signed-off-by: Juan Antonio Pedreira Martos <juanpm1@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>