busybox: rename busybox-update to busybox-update-config

The original name busybox-update is confusing as it only updates a
configuration file.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/busybox/busybox.mk

@@ -187,5 +187,5 @@ busybox-menuconfig busybox-xconfig busybox-gconfig: busybox-patch
 	rm -f $(BUSYBOX_DIR)/.stamp_built
 	rm -f $(BUSYBOX_DIR)/.stamp_target_installed
 
-busybox-update:
+busybox-update-config:
 	cp -f $(BUSYBOX_BUILD_CONFIG) $(BUSYBOX_CONFIG_FILE)