fs/ntfs3: fix an error code in ntfs_get_acl_ex()

The ntfs_get_ea() function returns negative error codes or on success
it returns the length.  In the original code a zero length return was
treated as -ENODATA and results in a NULL return.  But it should be
treated as an invalid length and result in an PTR_ERR(-EINVAL) return.

Fixes: be71b5cb ("fs/ntfs3: Add attrib operations")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>