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: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>