powerpc/mm: Avoid avoidable void* pointer

Change pgdir from a void to real type.  Having this as a void is
stupid and has already caused 1 bug.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/hash_utils_64.c

@@ -1070,7 +1070,7 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
 		  unsigned long access, unsigned long trap)
 {
 	unsigned long vsid;
-	void *pgdir;
+	pgd_t *pgdir;
 	pte_t *ptep;
 	unsigned long flags;
 	int rc, ssize, local = 0;