irqchip: orion: use handle_edge_irq on bridge irqs

Bridge irqs are edge-triggered, i.e. they get asserted on low-to-high
transitions and not on the level of the downstream interrupt line.
This replaces handle_level_irq by the more appropriate handle_edge_irq.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Cc: <stable@vger.kernel.org>: f56c0738b5c2: "irqchip: orion: clear bridge cause register on init"
Cc: <stable@vger.kernel.org> # v3.10+
Signed-off-by: Jason Cooper <jason@lakedaemon.net>