ARM: dts: imx6sx: fix irq for pcie bridge

Use the correct IRQ line for the MSI controller in the PCIe host
controller. Apparently a different IRQ line is used compared to other
i.MX6 variants. Without this change MSI IRQs aren't properly propagated
to the upstream interrupt controller.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Fixes: b1d17f68

 ("ARM: dts: imx: add initial imx6sx device tree source")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>