V4L/DVB (13331): mxl5005s: provide ability to override QAM gain for HVR-1600

The HVR-1600 doesn't use the standard mechanism for computing the gain when
in QAM mode, instead always forcing it to be 0x02.  Provide the ability to
override the algorithm on a per-board basis.

This change results in an improvement of 0.4-0.6 dB for QAM tuning.

This work was sponsored by ONELAN Limited.

Cc: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/cx18/cx18-dvb.c b/drivers/media/video/cx18/cx18-dvb.c
index f402e79..54a6fd3 100644
--- a/drivers/media/video/cx18/cx18-dvb.c
+++ b/drivers/media/video/cx18/cx18-dvb.c
@@ -61,6 +61,7 @@
 	.top		 = MXL5005S_TOP_25P2,
 	.mod_mode        = MXL_DIGITAL_MODE,
 	.if_mode         = MXL_ZERO_IF,
+	.qam_gain        = 0x02,
 	.AgcMasterByte   = 0x00,
 };