V4L/DVB (3423): Fix cx88 error messages on balance change

There is an error in the cx88 code that causes this message in the syslog when
balance is changed at full volume:
Mar  4 18:35:08 ian2 kernel: cx88[0]: irq pci [0x1] vid*
Mar  4 18:35:39 ian2 last message repeated 348 times
Mar  4 18:36:01 ian2 last message repeated 564 times
... and so on
The attached patch cures this problem.

Signed-off-by: Ian Pickworth <ian@pickworth.me.uk>
Signed-off-by: Marcin Rudowski <mar_rud@poczta.onet.pl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/cx88/cx88.h

@@ -63,7 +63,7 @@
 /* need "shadow" registers for some write-only ones ... */
 #define SHADOW_AUD_VOL_CTL           1
 #define SHADOW_AUD_BAL_CTL           2
-#define SHADOW_MAX                   2
+#define SHADOW_MAX                   3
 
 /* FM Radio deemphasis type */
 enum cx88_deemph_type {