ARM: dts: imx7: Drop reset-names property for mipi_csi node

The reset-names property isn't defined by the nxp,imx7-mipi-csi2.yaml
binding, and isn't used by the corresponding driver as it acquires the
reset with a NULL ID. Drop it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>