arm: vgic: Use find_first_bit instead of find_next_bit when possible

arm: vgic: Use find_first_bit instead of find_next_bit when possible

find_next_bit(foo, sz, 0) is equivalent to find_first_bit(foo, sz). The
latter is easier to understand. Some architecture may also have a
optimized version of find_first_bit(...). So replace the occurrence of
find_next_bit in vgic_vcpu_pending_irq()."

Signed-off-by: Artem Mygaiev <artem_mygaiev@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>