arm64: dts: imx8mp-skov-revb-mi1010ait-1cp1: Assign "media_isp" clock rate

Commit 2d39b78e ("arm64: dts: imx8mp: Add DT nodes for the two ISPs")
added a new phandle to the "assigned-clocks" property of media_blk_ctrl
node just before the phandle for "video_pll1" clock in i.MX8MP SoC device
tree so that "media_isp" clock rate is assigned to 500MHz by default.
However, it missed updating this relevant board device tree where the
relevant "assigned-clock-rates" property is changed to set a new rate
for "video_pll1" clock.  This causes the "media_isp" clock rate being
wrongly set to the "video_pll1" clock rate and the "video_pll1" clock
rate being untouched.  Fix this by assigning "media_isp" clock rate
explicitly to 500MHz in this board device tree.

Fixes: 2d39b78e ("arm64: dts: imx8mp: Add DT nodes for the two ISPs")
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>