arm64: dts: imx8mp: Fix assigned-clocks for second CSI2

The first CSI2 pixel clock are supplied from IMX8MP_CLK_MEDIA_CAM1_PIX_ROOT,
the second CSI2 pixel clock are supplied from IMX8MP_CLK_MEDIA_CAM2_PIX_ROOT,
both clock are supplied from SYS_PLL2 and configured using assigned-clock DT
properties. Each CSI2 DT node configures its IMX8MP_CLK_MEDIA_CAMn_PIX_ROOT
clock. This used to be the case until likely a copy-paste error in commit
f78835d1 ("arm64: dts: imx8mp: reparent MEDIA_MIPI_PHY1_REF to CLK_24M")
which changed the second CSI2 node to configure IMX8MP_CLK_MEDIA_CAM1_PIX_ROOT
using its assigned-clocks property.

Fix the second CSI2 assigned-clock property back to the original correct
IMX8MP_CLK_MEDIA_CAM2_PIX_ROOT .

Fixes: f78835d1 ("arm64: dts: imx8mp: reparent MEDIA_MIPI_PHY1_REF to CLK_24M")
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>