xfs: fix incorrect test in xfs_alloc_ag_vextent_lastblock

When I lifted the code in xfs_alloc_ag_vextent_lastblock out of a loop,
I forgot to convert all the accesses to len to be pointer dereferences.

Coverity-id: 1457918
Fixes: 5113f8ec ("xfs: clean up weird while loop in xfs_alloc_ag_vextent_near")
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_alloc.c

@@ -1514,7 +1514,7 @@ xfs_alloc_ag_vextent_lastblock(
 	 * maxlen, go to the start of this block, and skip all those smaller
 	 * than minlen.
 	 */
-	if (len || args->alignment > 1) {
+	if (*len || args->alignment > 1) {
 		acur->cnt->bc_ptrs[0] = 1;
 		do {
 			error = xfs_alloc_get_rec(acur->cnt, bno, len, &i);