swiotlb: Expose swiotlb_nr_tlb function to modules

As a mechanism to detect whether SWIOTLB is enabled or not.
We also fix the spelling - it was swioltb instead of
swiotlb.

CC: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
[v1: Ripped out swiotlb_enabled]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 8e964b9..4864e5d 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -153,7 +153,7 @@
 	char *m = NULL;
 	unsigned int repeat = 3;
 
-	nr_tbl = swioltb_nr_tbl();
+	nr_tbl = swiotlb_nr_tbl();
 	if (nr_tbl)
 		xen_io_tlb_nslabs = nr_tbl;
 	else {