ASoC: twl6040: Correct supported number of playback channels

twl6040 supports 5 playback, and 2 capture channels

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>