configs: stm32f769-disco: Fix console cmdline

The Linux cmdline encoded in the defconfig is wrong, the
STM32 USART driver registers as ttySTM0 not ttyS0.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/configs/stm32f769-disco_defconfig b/configs/stm32f769-disco_defconfig
index 5be221a..9edda0e 100644
--- a/configs/stm32f769-disco_defconfig
+++ b/configs/stm32f769-disco_defconfig
@@ -18,7 +18,7 @@
 CONFIG_AUTOBOOT_PROMPT="Hit SPACE in %d seconds to stop autoboot.\n"
 CONFIG_AUTOBOOT_STOP_STR=" "
 CONFIG_USE_BOOTARGS=y
-CONFIG_BOOTARGS="console=ttyS0,115200 earlyprintk consoleblank=0 ignore_loglevel"
+CONFIG_BOOTARGS="console=ttySTM0,115200n8 earlyprintk consoleblank=0 ignore_loglevel"
 CONFIG_SYS_PBSIZE=1050
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_CYCLIC_MAX_CPU_TIME_US=8000