configs: stm32f746-disco: Fix stm32f746-disco boot

Since commit 8f651ca60ba1 ("pinctrl: stm32: Add get_pins_count() ops")
stm32f746-disco can't boot.

This is due to new memory allocation into STM32 pinctrl driver,
increase SYS_MALLOC_F_LEN from 0xC00 to 0xE00.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/configs/stm32f746-disco_defconfig b/configs/stm32f746-disco_defconfig
index 1bf3a7c..121e962 100644
--- a/configs/stm32f746-disco_defconfig
+++ b/configs/stm32f746-disco_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_STM32=y
 CONFIG_SYS_TEXT_BASE=0x08008000
-CONFIG_SYS_MALLOC_F_LEN=0xC00
+CONFIG_SYS_MALLOC_F_LEN=0xE00
 CONFIG_STM32F7=y
 CONFIG_TARGET_STM32F746_DISCO=y
 CONFIG_ENV_VARS_UBOOT_CONFIG=y