powerpc/mm: Fix stupid bug in subpge protection handling

Commit d28513bc7f675d28b479db666d572e078ecf182d ("Fix bug in pagetable
cache cleanup with CONFIG_PPC_SUBPAGE_PROT"), itself a fix for
breakage caused by an earlier clean up patch of mine, contains a
stupid bug.  I changed the parameters of the subpage_protection()
function, but failed to update one of the callers.

This patch fixes it, and replaces a void * with a typed pointer so
that the compiler will warn on such an error in future.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/hash_utils_64.c

@@ -879,7 +879,7 @@ static inline int subpage_protection(struct mm_struct *mm, unsigned long ea)
  */
 int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
 {
-	void *pgdir;
+	pgd_t *pgdir;
 	unsigned long vsid;
 	struct mm_struct *mm;
 	pte_t *ptep;
@@ -1025,7 +1025,7 @@ int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
 	else
 #endif /* CONFIG_PPC_HAS_HASH_64K */
 	{
-		int spp = subpage_protection(pgdir, ea);
+		int spp = subpage_protection(mm, ea);
 		if (access & spp)
 			rc = -2;
 		else