OMAP: DSS2: clear spurious SYNC_LOST_DIGIT interrupts

When DSS transitions from off mode to on VENC may generate a spurious
SYNC_LOST_DIGIT error. Just ack it when restoring the context. Also
restore IRQENABLE last to avoid triggering interrupts before the
context is fully restored.

Signed-off-by: Ville Syrjälä <ville.syrjala@nokia.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>