[media] xc5000: delay tuner sleep to 5 seconds

Some drivers, like au0828 are very sensitive to tuner sleep and may
break if the sleep happens too fast. Also, by keeping the tuner alive
for a while could speedup tuning process during channel scan. So,
change the logic to delay the actual sleep to 5 seconds after its
command.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>