stm32/boards: Change default LSI_VALUE to 32000 for F4 MCUs.

In the STM32 HAL libraries, the default value for LSI_VALUE for F4 MCUs is
32 kHz.

Signed-off-by: David Lechner <david@pybricks.com>

ports/stm32/boards/stm32f4xx_hal_conf_base.h

@@ -88,7 +88,7 @@
 
 // Oscillator values in Hz
 #define HSI_VALUE (16000000)
-#define LSI_VALUE (40000)
+#define LSI_VALUE (32000)
 
 // SysTick has the highest priority
 #define TICK_INT_PRIORITY (0x00)