sh: convert nommu io{re,un}map() to static inline functions

Recently, nommu iounmap() was converted from a static inline function to a
macro again, basically reverting commit 4580ba4a ("sh: Convert
iounmap() macros to inline functions").  With -Werror, this leads to build
failures like:

    drivers/iio/adc/xilinx-ams.c: In function `ams_iounmap_ps':
    drivers/iio/adc/xilinx-ams.c:1195:14: error: unused variable `ams' [-Werror=unused-variable]
     1195 |  struct ams *ams = data;
	  |              ^~~

Fix this by replacing the macros for ioremap() and iounmap() by static
inline functions, based on <asm-generic/io.h>.

Link: https://lkml.kernel.org/r/8d1b1766260961799b04035e7bc39a7f59729f72.1655708312.git.geert+renesas@glider.be
Fixes: 13f1fc87 ("sh: move the ioremap implementation out of line")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/sh/include/asm/io.h

@@ -271,8 +271,12 @@ static inline void __iomem *ioremap_prot(phys_addr_t offset, unsigned long size,
 #endif /* CONFIG_HAVE_IOREMAP_PROT */
 
 #else /* CONFIG_MMU */
-#define iounmap(addr)		do { } while (0)
-#define ioremap(offset, size)	((void __iomem *)(unsigned long)(offset))
+static inline void __iomem *ioremap(phys_addr_t offset, size_t size)
+{
+	return (void __iomem *)(unsigned long)offset;
+}
+
+static inline void iounmap(volatile void __iomem *addr) { }
 #endif /* CONFIG_MMU */
 
 #define ioremap_uc	ioremap