xen/grant-table: Fix incorrect gnttab_dma_free_pages() pr_debug message

If a call to xenmem_reservation_increase() in gnttab_dma_free_pages()
fails it triggers a message "Failed to decrease reservation..." which
should be "Failed to increase reservation..."

Fixes: 9bdc7304 ('xen/grant-table: Allow allocating buffers suitable for DMA')
Reported-by: Ross Philipson <ross.philipson@oracle.com>
Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Mark Kanda <mark.kanda@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/grant-table.c

@@ -914,7 +914,7 @@ int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args)
 
 	ret = xenmem_reservation_increase(args->nr_pages, args->frames);
 	if (ret != args->nr_pages) {
-		pr_debug("Failed to decrease reservation for DMA buffer\n");
+		pr_debug("Failed to increase reservation for DMA buffer\n");
 		ret = -EFAULT;
 	} else {
 		ret = 0;