irqchip/aspeed-scu: Replace update_bits with write_bits.

The interrupt status bits are cleared by writing 1, we should force a
write to clear the interrupt without checking if the value has changed.

Fixes: 04f60590 ("irqchip: Add Aspeed SCU interrupt controller")
Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211124094348.11621-1-billy_tsai@aspeedtech.com
Cc: stable@vger.kernel.org