sh: Convert iounmap() macros to inline functions

Macro iounmap() do nothing, but that results in
unused variable warnings all over the place.
This patch convert it to inline to avoid warning

We will get this warning without this patch

	${LINUX}/drivers/thermal/broadcom/ns-thermal.c:78:21: \
	  warning: unused variable 'ns_thermal' [-Wunused-variable]
	struct ns_thermal *ns_thermal = platform_get_drvdata(pdev);
	^~~~~~~~~~

Fixes: 98c90e5e ("sh: remove __iounmap")
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Rich Felker <dalias@libc.org>

arch/sh/include/asm/io.h

@@ -328,7 +328,7 @@ __ioremap_mode(phys_addr_t offset, unsigned long size, pgprot_t prot)
 #else
 #define __ioremap(offset, size, prot)		((void __iomem *)(offset))
 #define __ioremap_mode(offset, size, prot)	((void __iomem *)(offset))
-#define iounmap(addr)				do { } while (0)
+static inline void iounmap(void __iomem *addr) {}
 #endif /* CONFIG_MMU */
 
 static inline void __iomem *ioremap(phys_addr_t offset, unsigned long size)