[media] cx23885-alsa: fix a false gcc warning at dprintk()

Change dprintk logic to avoid the following warning:
drivers/media/pci/cx23885/cx23885-alsa.c: In function 'cx23885_audio_register':
drivers/media/pci/cx23885/cx23885-alsa.c:515:2: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>