USB: Makefile fix for previous patch

drivers/usb/core/Makefile

@@ -2,10 +2,10 @@
 # Makefile for USB Core files and filesystem
 #
 
-export-objs	:= usb.o hcd.o hcd-pci.o urb.o message.o file.o
+export-objs	:= usb.o hcd.o hcd-pci.o urb.o message.o file.o buffer.o
 
 usbcore-objs	:= usb.o usb-debug.o hub.o hcd.o urb.o message.o \
-			config.o file.o
+			config.o file.o buffer.o
 
 ifeq ($(CONFIG_PCI),y)
 	usbcore-objs	+= hcd-pci.o