[media] saa7164: silence GCC warnings

Compiling the saa7164 driver without CONFIG_VIDEO_ADV_DEBUG set triggers
these GCC warnings:
    drivers/media/pci/saa7164/saa7164-encoder.c:1301:12: warning: ‘saa7164_g_register’ defined but not used [-Wunused-function]
    drivers/media/pci/saa7164/saa7164-encoder.c:1314:12: warning: ‘saa7164_s_register’ defined but not used [-Wunused-function]
Silence these warnings by wrapping these two functions in an "#ifdef
CONFIG_VIDEO_ADV_DEBUG" and "#endif" pair.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>