arm64: dts: imx8mm: Remove video_pll1 clock rate from clk node

There are two clock-rate assignments for video_pll1, and the
only one it should really have belongs inside the lcdif node,
since it's the only consumer of this clock.  Remove it from
the clk node.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de> # Kontron BL i.MX8MM
Signed-off-by: Shawn Guo <shawnguo@kernel.org>