dma-mapping: don't BUG when calling dma_map_resource on RAM

Use WARN_ON_ONCE to print a stack trace and return a proper error
code instead.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NRobin Murphy <robin.murphy@arm.com>
Tested-by: NMarek Szyprowski <m.szyprowski@samsung.com>

include/linux/dma-mapping.h

@@ -353,7 +353,8 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
 	BUG_ON(!valid_dma_direction(dir));
 
 	/* Don't allow RAM to be mapped */
-	BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
+	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
+		return DMA_MAPPING_ERROR;
 
 	if (dma_is_direct(ops))
 		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);