ARM: dts: imx6qdl-nitrogen6_som2: fix PCIe reset

Previous value was a bad copy of nitrogen6_max device tree.

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Fixes: 3faa1bb2

 ("ARM: dts: imx: add Boundary Devices Nitrogen6_SOM2 support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>