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 4580ba4ad2e6b8dd ("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/8d1b1[e-mail]
Fixes: 13f1fc870dd74713 ("sh: move the ioremap implementation out of line")
Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Reported-by: Jonathan Cameron <[e-mail]>
Acked-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/sh/include/asm/io.h

···
 #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