gitconfig: Match the Change-Id line more exactly

Change-Id: I5ac267770bc5b43dd1435e75ab0fcbde0d88b664
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/1487
Reviewed-by: Anton Kochkov <anton.kochkov@gmail.com>
Tested-by: build bot (Jenkins)

util/gitconfig/commit-msg

@@ -37,7 +37,7 @@ add_ChangeId() {
 	fi
 
 	# Does Change-Id: already exist? if so, exit (no change).
-	if grep -i '^Change-Id:' "$MSG" >/dev/null
+	if grep -i '^Change-Id: I[0-9a-f]\{40\}$' "$MSG" >/dev/null
 	then
 		return
 	fi