V4L/DVB (12407): em28xx: Adjust Silvercrest xtal frequency

We don't know the xtal frequency of Silvercrest, but we need to have
some value in order to allow controlling the frame rate frequency. The
value is probably still wrong, since the manufacturer announces this
device as being capable of 30fps, but the maximum we can get is
13.5 fps.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-cards.c

@@ -1785,7 +1785,7 @@ static int em28xx_hint_sensor(struct em28xx *dev)
 		dev->em28xx_sensor = EM28XX_MT9V011;
 		dev->sensor_xres = 640;
 		dev->sensor_yres = 480;
-		dev->sensor_xtal = 6300000;
+		dev->sensor_xtal = 12150000;
 
 		/* probably means GRGB 16 bit bayer */
 		dev->vinmode = 0x0d;