ARM: dts: imx7d: Fix UART2 base address

The UART2 memory space starts at address 0x30890000 (UART2_URXD).

Fix it so that UART2 can be used.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Fixes: 94967345 ("ARM: dts: add imx7d soc dtsi file")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>