UCG: track master instead of a specific commit id

Author: alex--m

.gitmodules

@@ -1,3 +1,4 @@
 [submodule "ucg"]
 	path = src/ucg
 	url = https://github.com/openucx/xucg.git
+	branch = master

autogen.sh

@@ -33,7 +33,7 @@ mkdir -p config/m4 config/aux
 
 if [ "X$with_ucg" = "Xyes" ]
 then
-	git submodule update --init --recursive
+	git submodule update --init --recursive --remote
 fi
 
 autoreconf -v --install || exit 1