Fix problem with multiple versions of uboot

If multiple versions of the uboot deb package exist on the apt
repo the makefile would barf when trying to unpack multiple files

Change-Id: Iede2280375d9fb9cf2ac3baece0f929785af516b
diff --git a/bootloader.mk b/bootloader.mk
index 3f01535..815e1c6 100644
--- a/bootloader.mk
+++ b/bootloader.mk
@@ -34,7 +34,8 @@
 $(PRODUCT_OUT)/u-boot.imx: fetch-uboot | out-dirs
 endif
 	$(LOG) u-boot extract
-	find $(PRODUCT_OUT)/packages -name 'uboot-imx*$(USERSPACE_ARCH)*.deb' | xargs \
+	find $(PRODUCT_OUT)/packages -name 'uboot-imx*$(USERSPACE_ARCH)*.deb' | \
+	sort -n | tail -1 | xargs \
 	dpkg --fsys-tarfile | \
 	tar --strip-components 2 -C $(PRODUCT_OUT) -xf - ./boot/u-boot.imx
 	$(LOG) u-boot finished