ASoC: ak4641: Remove unused AK4641_CACHEREGNUM define

The last user was removed in commit 4f534777 ("ASoC: ak4641: Convert to
direct regmap API usage").
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/ak4641.h

@@ -36,6 +36,4 @@
 #define AK4641_EQHI		0x12
 #define AK4641_BTIF		0x13
 
-#define AK4641_CACHEREGNUM	0x14
-
 #endif