irqchip/versatile-fpga: Apply clear-mask earlier

commit 6a214a28 upstream.

Clear its own IRQs before the parent IRQ get enabled, so that the
remaining IRQs do not accidentally interrupt the parent IRQ controller.

This patch also fixes a reboot bug on OX820 SoC, where the remaining
rps-timer IRQ raises a GIC interrupt that is left pending. After that,
the rps-timer IRQ is cleared during driver initialization, and there's
no IRQ left in rps-irq when local_irq_enable() is called, which evokes
an error message "unexpected IRQ trap".

Fixes: bdd272cb ("irqchip: versatile FPGA: support cascaded interrupts from DT")
Signed-off-by: Sungbo Eo <mans0n@gorani.run>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200321133842.2408823-1-mans0n@gorani.run


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>