OMAP: McBSP: Use appropriate value for startup delay

Increasing startup delay value as worst case:
 CLKSRG*2 = 8000khz: (1/8000) * 2 * 2 usec

Although, 100us may give enough time for two CLKSRG,
due to some unknown PM related, clock gating etc. reason,
this patch increases it to 500us.

Signed-off-by: Eduardo Valentin <eduardo.valentin@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>