sh: prevent warnings when using iounmap

When building drm/exynos for sh, as part of an allmodconfig build, the
following warning triggered:

  exynos7_drm_decon.c: In function `decon_remove':
  exynos7_drm_decon.c:769:24: warning: unused variable `ctx'
    struct decon_context *ctx = dev_get_drvdata(&pdev->dev);

The ctx variable is only used as argument to iounmap().

In sh - allmodconfig CONFIG_MMU is not defined
so it ended up in:

\#define __iounmap(addr)	do { } while (0)
\#define iounmap		__iounmap

Fix the warning by introducing a static inline function for iounmap.

This is similar to several other architectures.

Link: http://lkml.kernel.org/r/20190622114208.24427-1-sam@ravnborg.org
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/sh/include/asm/io.h

@@ -369,7 +369,11 @@ static inline int iounmap_fixed(void __iomem *addr) { return -EINVAL; }
 
 #define ioremap_nocache	ioremap
 #define ioremap_uc	ioremap
-#define iounmap		__iounmap
+
+static inline void iounmap(void __iomem *addr)
+{
+	__iounmap(addr);
+}
 
 /*
  * Convert a physical pointer to a virtual kernel pointer for /dev/mem