board: beacon: imx8mn: Let clock system enable UART clock

Now that the UART driver can enable the required clocks, remove
the hard-coded clock enable.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>

board/beacon/imx8mn/spl.c

@@ -111,8 +111,6 @@ int board_early_init_f(void)
 	/* Claiming pwm pins prevents LCD flicker during startup*/
 	imx_iomux_v3_setup_multiple_pads(pwm_pads, ARRAY_SIZE(pwm_pads));
 
-	init_uart_clk(1);
-
 	return 0;
 }