OMAP3: McBSP: Lower the maximum buffersize for McBSP1, 3, 4, 5

Do not allow applications to use the full buffer found on
McBSP1,3,4,5. Using the full buffer in threshold mode causes
the McBSP buffer to run dry, which can be observed as channels
are switching (in reality the channels are shifting).

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>