[ARM] 4002/1: S3C24XX: leave parent IRQs unmasked

Do not bother masking/unmasking the parent IRQ
for the mulitplexed EINT irqs, as masking the
leaf seems to be fine.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>