ext4: error handling fix in ext4_ext_convert_to_initialized()

When allocated is unsigned it breaks the error handling at the end
of the function when we call:
	allocated = ext4_split_extent(...);
	if (allocated < 0)
		err = allocated;

I've made it a signed int instead of unsigned.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/extents.c

@@ -2928,7 +2928,8 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 	struct ext4_extent zero_ex;
 	struct ext4_extent *ex;
 	ext4_lblk_t ee_block, eof_block;
-	unsigned int allocated, ee_len, depth;
+	unsigned int ee_len, depth;
+	int allocated;
 	int err = 0;
 	int split_flag = 0;