ARM: dts: imx7s-warp: Drop undefined property in mipi_csi node

The fsl,csis-hs-settle property isn't defined by the
nxp,imx7-mipi-csi2.yaml binding, and isn't parsed by the corresponding
driver. Drop it.

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