V4L/DVB (4759): Cx88: use external adc for rca audio inputs on the ASUS PVR-416

For the ASUS PVR-416, the external adc must be used for
the rca audio inputs, but television / radio inputs use
the internal adc.
Thanks to Alex Deucher for lending his card to me.
Signed-off-by: NMichael Krufky <mkrufky@linuxtv.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/cx88/cx88-cards.c

@@ -357,6 +357,7 @@ struct cx88_board cx88_boards[] = {
 			.type   = CX88_VMUX_SVIDEO,
 			.vmux   = 2,
 			.gpio0  = 0x0000fde6, // 0x0000fda6 L,R RCA audio in?
+			.extadc = 1,
 		}},
 		.radio = {
 			.type   = CX88_RADIO,