u-boot: fix wrong syntax in Makefile

Patch by Markus Heidelberg <markus.heidelberg@web.de>

Some $(call insert_define, ..., ...) calls were lacking the comma after
the variable. That didn't lead to a syntax error but it didn't have any
effect on the output u-boot/include/config.h

target/u-boot/Makefile.in

@@ -98,16 +98,16 @@ ifneq ($(strip $(BR2_TARGET_UBOOT_ETHADDR)),"")
 	$(call insert_define, "CONFIG_ETHADDR", $(BR2_TARGET_UBOOT_ETHADDR))
 endif
 ifneq ($(strip $(BR2_TARGET_UBOOT_ETH1ADDR)),"")
-	$(call insert_define "CONFIG_ETH2ADDR", $(BR2_TARGET_UBOOT_ETH1ADDR))
+	$(call insert_define, "CONFIG_ETH2ADDR", $(BR2_TARGET_UBOOT_ETH1ADDR))
 endif
 ifneq ($(strip $(BR2_TARGET_UBOOT_BOOTARGS)),"")
-	$(call insert_define "CONFIG_BOOTARGS", $(BR2_TARGET_UBOOT_BOOTARGS))
+	$(call insert_define, "CONFIG_BOOTARGS", $(BR2_TARGET_UBOOT_BOOTARGS))
 endif
 ifneq ($(strip $(BR2_TARGET_UBOOT_BOOTCMD)),"")
-	$(call insert_define "CONFIG_BOOTCOMMAND", $(BR2_TARGET_UBOOT_BOOTCMD))
+	$(call insert_define, "CONFIG_BOOTCOMMAND", $(BR2_TARGET_UBOOT_BOOTCMD))
 endif
 ifneq ($(strip $(BR2_TARGET_UBOOT_SILENT)),"")
-	$(call insert_define "CONFIG_SILENT_CONSOLE", "")
+	$(call insert_define, "CONFIG_SILENT_CONSOLE", "")
 endif
 	@echo "#endif /* __BR2_ADDED_CONFIG_H */" >> $(U_BOOT_INC_CONF_FILE)
 	touch $@