xen/swiotlb: For early initialization, return zero on success.

If everything is setup properly we would return -ENOMEM since
rc by default is set to that value. Lets not do that and return
a proper return code.

Note: The reason the early code needs this special treatment
is that it SWIOTLB library call does not return anything (and
had it failed it would call panic()) - but our function does.
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/swiotlb-xen.c

@@ -230,9 +230,10 @@ int __ref xen_swiotlb_init(int verbose, bool early)
 		goto error;
 	}
 	start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
-	if (early)
+	if (early) {
 		swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs, verbose);
-	else
+		rc = 0;
+	} else
 		rc = swiotlb_late_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs);
 	return rc;
 error: