[media] cx25840: fix regression in HVR-1800 analog audio

The refactoring of the cx25840 driver to support the cx23888 caused breakage
with the existing support for cx23885/cx23887 analog audio support.  Tweak
the code so that it only uses the code if it really is a cx23888 instead of
applying it to all cx2388x based devices.

Validated with the following boards:

HVR-1800 retail (0070:7801)
HVR-1800 OEM (0070:7809)
HVR_1850 retail	(0070:8541)

Thanks to Steven Toth and Hauppauge for	loaning	me various boards to
regression test with.
Reported-by: Jonathan <sitten74490@mypacks.net>
Thanks-to: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Devin Heitmueler <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/cx25840/cx25840-core.c

@@ -1250,7 +1250,7 @@ static int set_input(struct i2c_client *client, enum cx25840_video_input vid_inp
 		cx25840_write4(client, 0x8d0, 0x1f063870);
 	}
 
-	if (is_cx2388x(state)) {
+	if (is_cx23888(state)) {
 		/* HVR1850 */
 		/* AUD_IO_CTRL - I2S Input, Parallel1*/
 		/*  - Channel 1 src - Parallel1 (Merlin out) */