Fix the USART6 default baudrate to match the IO bootloader.

nuttx/configs/px4fmuv2/nsh/defconfig

@@ -188,6 +188,7 @@ CONFIG_STM32_PWR=y
 CONFIG_STM32_TIM1=y
 CONFIG_STM32_TIM8=n
 CONFIG_STM32_USART1=y
+# Mostly owned by the px4io driver, but uploader needs this
 CONFIG_STM32_USART6=y
 # We use our own driver, but leave this on.
 CONFIG_STM32_ADC1=y
@@ -260,7 +261,7 @@ CONFIG_USART1_BAUD=115200
 CONFIG_USART2_BAUD=115200
 CONFIG_USART3_BAUD=115200
 CONFIG_UART4_BAUD=115200
-CONFIG_USART6_BAUD=9600
+CONFIG_USART6_BAUD=115200
 CONFIG_UART7_BAUD=115200
 CONFIG_UART8_BAUD=57600