tile: don't panic on iomap

I think panic on iomap is there just for debugging.
If we return NULL instead, the generic pci_iomap will
DTRT so we don't need to roll our own.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

arch/tile/include/asm/io.h

@@ -204,7 +204,8 @@ static inline long ioport_panic(void)
 
 static inline void __iomem *ioport_map(unsigned long port, unsigned int len)
 {
-	return (void __iomem *) ioport_panic();
+	pr_info("ioport_map: mapping IO resources is unsupported on tile.\n");
+	return NULL;
 }
 
 static inline void ioport_unmap(void __iomem *addr)