swiotlb-xen: Convert to use macro

Rather than using static int max_dma_bits, this
can be coverted to use as macro.
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/swiotlb-xen.c

@@ -38,6 +38,7 @@
 #include <asm/xen/page-coherent.h>
 
 #include <trace/events/swiotlb.h>
+#define MAX_DMA_BITS 32
 /*
  * Used to do a quick range check in swiotlb_tbl_unmap_single and
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
@@ -114,8 +115,6 @@ static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
 	return 0;
 }
 
-static int max_dma_bits = 32;
-
 static int
 xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
 {
@@ -135,7 +134,7 @@ xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
 				p + (i << IO_TLB_SHIFT),
 				get_order(slabs << IO_TLB_SHIFT),
 				dma_bits, &dma_handle);
-		} while (rc && dma_bits++ < max_dma_bits);
+		} while (rc && dma_bits++ < MAX_DMA_BITS);
 		if (rc)
 			return rc;