irqchip/mips-gic: Use for_each_set_bit to iterate over local IRQs

The MIPS GIC driver has previously iterated over bits set in a bitmap
representing pending local IRQs by calling find_first_bit, clearing that
bit then calling find_first_bit again until all bits are clear. If
multiple interrupts are pending then this is wasteful, as find_first_bit
will have to loop over the whole bitmap from the start. Use the
for_each_set_bit macro which performs exactly what we need here instead.
It will use find_next_bit and thus only scan over the relevant part of
the bitmap, and it makes the intent of the code clearer.

This makes the same change for local interrupts that commit cae750ba


("irqchip: mips-gic: Use for_each_set_bit to iterate over IRQs") made
for shared interrupts.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-mips@linux-mips.org
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/20160913165427.31686-1-paul.burton@imgtec.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>