ARM: dts: imx7d-zii-rpu2: Fix incorrrect 'stdout-path'

RPU2 uses UART2 as a serial console and UART1 is not used at all. Fix
incorrrectly specified 'stdout-path' to reflect that.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>