ARM: OMAP: McBSP: Fix legacy interrupts to clear their status

If XSYNCERR or RSYNCERR interrupts are enabled, they are never
cleared causing the IRQ handler to be continuously called.
This patch clears the IRQs in question in the event they are
enabled and taken.

Signed-off-by: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>