ARM: dts: imx31: fix AVIC base address

commit af92305e upstream.

On i.MX31 AVIC interrupt controller base address is at 0x68000000.

The problem was shadowed by the AVIC driver, which takes the correct
base address from a SoC specific header file.

Fixes: d2a37b3d ("ARM i.MX31: Add devicetree support")
Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>