create-pull-request: Fix error on 2.0 versions of git

On 2.0 versions of git, the create-pull-request script exits with the
warning "No match for commit... Are you sure you pushed 'HEAD' there?".

This is due to a change in behavior where git used to guess the branch
you meant, but no longer does.  See the thread at
http://www.spinics.net/lists/git/msg233050.html for more information.

To accommodate the new behavior, if the COMMIT_ID is set to the default
of "HEAD", make it point explicitly to $BRANCH instead.

(From OE-Core rev: 7ee64ea60ede5477b2f9a355d93bdc556e6b7895)

Signed-off-by: Ben Shelton <ben.shelton@ni.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/create-pull-request

@@ -125,6 +125,10 @@ if [ -z "$BRANCH" ]; then
 	echo "NOTE: Assuming remote branch '$BRANCH', use -b to override."
 fi
 
+if [ "$COMMIT_ID" == "HEAD" ]; then
+	COMMIT_ID="$BRANCH"
+fi
+
 if [ -z "$REMOTE_URL" ]; then
 	echo "ERROR: Missing parameter -u, no git remote!"
 	usage