git-submodule: Avoid 'fatal: cannot describe' message

When "git submodule status" command tries to show the name of the
submodule HEAD revision more descriptively, but the submodule
repository lacked a suitable tag to do so, it leaked "fatal: cannot
describe" message to the UI.  Squelch it by using '--always'.

Signed-off-by: Ping Yin <pkufranky@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -327,7 +327,7 @@ set_name_rev () {
 		cd "$1" && {
 			git describe "$2" 2>/dev/null ||
 			git describe --tags "$2" 2>/dev/null ||
-			git describe --contains --tags "$2"
+			git describe --contains --tags --always "$2"
 		}
 	) )
 	test -z "$revname" || revname=" ($revname)"