ext4: fix the number of credits needed for ext4_ext_migrate()

The migration ioctl creates a temporary inode.  Since this inode is
never linked to a directory, we don't need to reserve journal credits
required for modifying the directory.
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: NJan Kara <jack@suse.cz>

fs/ext4/migrate.c

@@ -456,11 +456,14 @@ int ext4_ext_migrate(struct inode *inode)
 		 */
 		return retval;
 
+	/*
+	 * Worst case we can touch the allocation bitmaps, a bgd
+	 * block, and a block to link in the orphan list.  We do need
+	 * need to worry about credits for modifying the quota inode.
+	 */
 	handle = ext4_journal_start(inode, EXT4_HT_MIGRATE,
-					EXT4_DATA_TRANS_BLOCKS(inode->i_sb) +
-					EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3 +
-					EXT4_MAXQUOTAS_INIT_BLOCKS(inode->i_sb)
-					+ 1);
+		4 + EXT4_MAXQUOTAS_TRANS_BLOCKS(inode->i_sb));
+
 	if (IS_ERR(handle)) {
 		retval = PTR_ERR(handle);
 		return retval;