swiotlb: remove swiotlb_nr_tbl

All callers just use it to check if swiotlb is active at all, for which
they can just use is_swiotlb_active.  In the longer run drivers need
to stop using is_swiotlb_active as well, but let's do the simple step
first.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

kernel/dma/swiotlb.c

@@ -94,12 +94,6 @@ setup_io_tlb_npages(char *str)
 }
 early_param("swiotlb", setup_io_tlb_npages);
 
-unsigned long swiotlb_nr_tbl(void)
-{
-	return io_tlb_default_mem ? io_tlb_default_mem->nslabs : 0;
-}
-EXPORT_SYMBOL_GPL(swiotlb_nr_tbl);
-
 unsigned int swiotlb_max_segment(void)
 {
 	return io_tlb_default_mem ? max_segment : 0;
@@ -652,6 +646,7 @@ bool is_swiotlb_active(void)
 {
 	return io_tlb_default_mem != NULL;
 }
+EXPORT_SYMBOL_GPL(is_swiotlb_active);
 
 #ifdef CONFIG_DEBUG_FS