arm64: dts: ti: k3-am64-mcu: remove incorrect UART base clock rates

We found that (at least some versions of) the sci-fw set the base clock
rate for UARTs in the MCU domain to 96 MHz instead of the expected 48 MHz,
leading to incorrect baud rates when used from Linux.

As the 8250_omap driver will query the actual clock rate from the clk
driver when clock-frequency is unset, removing the incorrect property is
sufficient to fix the baud rate.

Fixes: 8abae938 ("arm64: dts: ti: Add support for AM642 SoC")
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20220419075157.189347-1-matthias.schiffer@ew.tq-group.com