V4L/DVB (6969): Avoid causing regressions for non-HVR950 boards

Only HVR950 has analog_gpio configured. It makes no sense to set gpio to 0 for
other boards. Better to add a test, while this var is not set for all xc3028
devices.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>