ASoC: ab8500-codec: Drop bank prefix from AB8500_GPIO_DIR4_REG register define

The AB8500_GPIO_DIR4_REG register define has the bank for the register in the
upper 8 bits and the register itself in the lower 8 bits. When passing it to
abx500_{set,get}_register_interruptible() the upper bits get truncated which
generates the following warning from sparse:
	sound/soc/codecs/ab8500-codec.c:1972:53: warning: cast truncates bits
	 from constant value (1013 becomes 13)
	sound/soc/codecs/ab8500-codec.c:1980:53: warning: cast truncates bits
	 from constant value (1013 becomes 13)

The bank is passed separately to abx500_{set,get}_register_interruptible() so
the code works fine as it is. Given that all users of AB8500_GPIO_DIR4_REG
always truncate the upper 8 bits just remove them from the define.

Also remove the unnecessary casts to u8.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>