linux-wandboard

MLK-13735 ARM: dtsi: imx7ulp: set the lpuart module clock to 48Mhz

The untrimmed chip firc clock is 50Mhz after manually tuning.
Now the trimmed chip firc clock is stable to 48Mhz, so change
the lpuart module clock rate to 48Mhz.

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>