sh: sh7786: Add explicit I/O cast to sh7786_mm_sel()

When compile-testing on arm:

    arch/sh/include/cpu-sh4/cpu/sh7786.h: In function ‘sh7786_mm_sel’:
    arch/sh/include/cpu-sh4/cpu/sh7786.h:135:21: warning: passing argument 1 of ‘__raw_readl’ makes pointer from integer without a cast [-Wint-conversion]
      return __raw_readl(0xFC400020) & 0x7;
			 ^~~~~~~~~~
    In file included from include/linux/io.h:25:0,
		     from arch/sh/include/cpu-sh4/cpu/sh7786.h:14,
		     from drivers/pinctrl/sh-pfc/pfc-sh7786.c:15:
    arch/arm/include/asm/io.h:113:21: note: expected ‘const volatile void *’ but argument is of type ‘unsigned int’
     #define __raw_readl __raw_readl
			 ^
    arch/arm/include/asm/io.h:114:19: note: in expansion of macro ‘__raw_readl’
     static inline u32 __raw_readl(const volatile void __iomem *addr)
		       ^~~~~~~~~~~

__raw_readl() on SuperH is a macro that casts the passed I/O address to
the correct type, while the implementations on most other architectures
expect to be passed the correct pointer type.

Add an explicit cast to fix this.

Note that this also gets rid of a sparse warning on SuperH:

    arch/sh/include/cpu-sh4/cpu/sh7786.h:135:16: warning: incorrect type in argument 1 (different base types)
    arch/sh/include/cpu-sh4/cpu/sh7786.h:135:16:    expected void const volatile [noderef] <asn:2>*<noident>
    arch/sh/include/cpu-sh4/cpu/sh7786.h:135:16:    got unsigned int
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>

arch/sh/include/cpu-sh4/cpu/sh7786.h

@@ -132,7 +132,7 @@ enum {
 
 static inline u32 sh7786_mm_sel(void)
 {
-	return __raw_readl(0xFC400020) & 0x7;
+	return __raw_readl((const volatile void __iomem *)0xFC400020) & 0x7;
 }
 
 #endif /* __CPU_SH7786_H__ */