af_packet: fix sparse warning

af_packet produces lots of these:
	net/packet/af_packet.c:384:39: warning: incorrect type in return expression (different modifiers)
	net/packet/af_packet.c:384:39:    expected struct page [pure] *
	net/packet/af_packet.c:384:39:    got struct page *

this seems to be because sparse does not realize that _pure
refers to function, not the returned pointer.

Tweak code slightly to avoid the warning.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -378,7 +378,7 @@ static void unregister_prot_hook(struct sock *sk, bool sync)
 		__unregister_prot_hook(sk, sync);
 }
 
-static inline __pure struct page *pgv_to_page(void *addr)
+static inline struct page * __pure pgv_to_page(void *addr)
 {
 	if (is_vmalloc_addr(addr))
 		return vmalloc_to_page(addr);