apple: Fix debug uart clock rate

The clock rate for the serial console on Apple M1 systems is 24 MHz
instead of 240 kHz.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
diff --git a/configs/apple_m1_defconfig b/configs/apple_m1_defconfig
index 433cc62..8583e4a 100644
--- a/configs/apple_m1_defconfig
+++ b/configs/apple_m1_defconfig
@@ -2,7 +2,7 @@
 CONFIG_ARCH_APPLE=y
 CONFIG_DEFAULT_DEVICE_TREE="t8103-j274"
 CONFIG_DEBUG_UART_BASE=0x235200000
-CONFIG_DEBUG_UART_CLOCK=240000
+CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_DEBUG_UART=y
 CONFIG_SYS_LOAD_ADDR=0x880000000
 CONFIG_USE_PREBOOT=y