uboot-mvebu: point to UBOOT_CONFIG when setting options

The BUILD_VARIANT might differ from UBOOT_CONFIG, so point to a file we
are actually changing. Being here let's call 'Build/Configure/U-Boot'
definition, instead of definig the same command. This'll be more future
proof, if U-Boot configuration procedure will change.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>

package/boot/uboot-mvebu/Makefile

@@ -42,11 +42,11 @@ UBOOT_TARGETS:= \
 Build/Exports:=$(Host/Exports)
 
 define Build/Configure
-	# enable additional options beyond clearfog_defconfig
-	echo CONFIG_NET_RANDOM_ETHADDR=y >> $(PKG_BUILD_DIR)/configs/$(BUILD_VARIANT)_defconfig
-	echo CONFIG_CMD_SETEXPR=y >> $(PKG_BUILD_DIR)/configs/$(BUILD_VARIANT)_defconfig
+	# enable additional options beyond <device>_defconfig
+	echo CONFIG_NET_RANDOM_ETHADDR=y >> $(PKG_BUILD_DIR)/configs/$(UBOOT_CONFIG)_defconfig
+	echo CONFIG_CMD_SETEXPR=y >> $(PKG_BUILD_DIR)/configs/$(UBOOT_CONFIG)_defconfig
 
-	+$(MAKE) $(PKG_JOBS) -C $(PKG_BUILD_DIR) $(UBOOT_CONFIGURE_VARS) $(UBOOT_CONFIG)_config
+	$(call Build/Configure/U-Boot)
 endef
 
 define Build/InstallDev