bananapro: bump U-Boot to version 2017.09

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/bananapro_defconfig

@@ -39,7 +39,7 @@ BR2_TARGET_ROOTFS_EXT2_4=y
 BR2_TARGET_UBOOT=y
 BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION=y
-BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2017.07"
+BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2017.09"
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="Bananapro"
 BR2_TARGET_UBOOT_NEEDS_DTC=y
 BR2_TARGET_UBOOT_NEEDS_PYLIBFDT=y