sh: pgtable-3level: Fix cast to pointer from integer of different size

If X2TLB=y (CPU_SHX2=y or CPU_SHX3=y, e.g. migor_defconfig), pgd_t.pgd
is "unsigned long long", causing:

    In file included from arch/sh/include/asm/pgtable.h:13,
		     from include/linux/pgtable.h:6,
		     from include/linux/mm.h:33,
		     from arch/sh/kernel/asm-offsets.c:14:
    arch/sh/include/asm/pgtable-3level.h: In function ‘pud_pgtable’:
    arch/sh/include/asm/pgtable-3level.h:37:9: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
       37 |  return (pmd_t *)pud_val(pud);
	  |         ^

Fix this by adding an intermediate cast to "unsigned long", which is
basically what the old code did before.

Fixes: 9cf6fa24 ("mm: rename pud_page_vaddr to pud_pgtable and make it return pmd_t *")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Daniel Palmer <daniel@thingy.jp>
Acked-by: Rob Landley <rob@landley.net>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Rich Felker <dalias@libc.org>

arch/sh/include/asm/pgtable-3level.h

@@ -34,7 +34,7 @@ typedef struct { unsigned long long pmd; } pmd_t;
 
 static inline pmd_t *pud_pgtable(pud_t pud)
 {
-	return (pmd_t *)pud_val(pud);
+	return (pmd_t *)(unsigned long)pud_val(pud);
 }
 
 /* only used by the stubbed out hugetlb gup code, should never be called */