Since we register as a chained handler, we need to take care of acking
the parent irq.  Current code had the acking disabled because just
acking the interrupt disables it on some interrupt controllers (like the
VIC used on Nomadik).  However, not acking at all is incorrect because
interrupt controllers like the GIC need an EOI indication, which is done
in the ack routine.

Solve this by maskacking and unmasking it appropriately, similar to how
handle_level_irq operates.
Acked-by: Alessandro Rubini <rubini@unipv.it>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>