ASoC: max98088 codec: Catch driver bugs for eq channel name

Move the EQ channel names to a separate array and iterate over it in
max98088_get_channel rather than duplicating the hardcoded channel
names. Add an error message if an invalid channel is passed and check
the error in the callers.

Also added a BUILD_BUG_ON to ensure that the eq_mode_name and controls
arrays are the same size.

Signed-off-by: Ryan Mallon <rmallon@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>