The driver never supported more than 2 channels because of
ep93xx_i2s_dma_data[] supporting only 1 DMA channel in each
direction.
Stop enabling two unused I2S controller FIFOs, this will simplify
future interrupt support.
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>