Clean up relay_alloc_page_array() slightly by using vzalloc rather than vmalloc and memset

We can optimize kernel/relay.c::relay_alloc_page_array() slightly by
using vzalloc. The patch makes these changes:

- use vzalloc instead of vmalloc+memset.
- remove redundant local variable 'array'.
- declare local 'pa_size' as const.

Cuts down nicely on both source and object-code size.

Signed-off-by: Jesper Juhl <[e-mail]>
Acked-by: Pekka Enberg <[e-mail]>
Acked-by: Mathieu Desnoyers <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/relay.c

···
  */
 static struct page **relay_alloc_page_array(unsigned int n_pages)
 {
-	struct page **array;
-	size_t pa_size = n_pages * sizeof(struct page *);
-
-	if (pa_size > PAGE_SIZE) {
-		array = vmalloc(pa_size);
-		if (array)
-			memset(array, 0, pa_size);
-	} else {
-		array = kzalloc(pa_size, GFP_KERNEL);
-	}
-	return array;
+	const size_t pa_size = n_pages * sizeof(struct page *);
+	if (pa_size > PAGE_SIZE)
+		return vzalloc(pa_size);
+	return kzalloc(pa_size, GFP_KERNEL);
 }
 
 /*