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/common/tuners/mxl5005s.h b/drivers/media/common/tuners/mxl5005s.h
index 7ac6815..fc8a1ff 100644
--- a/drivers/media/common/tuners/mxl5005s.h
+++ b/drivers/media/common/tuners/mxl5005s.h
@@ -108,6 +108,10 @@
 #define MXL_LOW_IF  1
 	u8 if_mode;
 
+	/* Some boards need to override the built-in logic for determining
+	   the gain when in QAM mode (the HVR-1600 is one such case) */
+	u8 qam_gain;
+
 	/* Stuff I don't know what to do with */
 	u8 AgcMasterByte;
 };