ipv6: mcast: make annotations for ip6_mc_msfget() consistent

Commit 931ca7ab ("ip*_mc_gsfget(): lift copyout of struct group_filter
into callers") adjusted the type annotations for ip6_mc_msfget() at its
declaration, but missed the type annotations at its definition.

Hence, sparse complains on ./net/ipv6/mcast.c:

  mcast.c:550:5: error: symbol 'ip6_mc_msfget' redeclared with different type \
  (incompatible argument 3 (different address spaces))

Make ip6_mc_msfget() annotations consistent, which also resolves this
warning from sparse:

  mcast.c:607:34: warning: incorrect type in argument 1 (different address spaces)
  mcast.c:607:34:    expected void [noderef] __user *to
  mcast.c:607:34:    got struct __kernel_sockaddr_storage *p

No functional change. No change in object code.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20201028115349.6855-1-lukas.bulwahn@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/mcast.c

@@ -548,7 +548,7 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf,
 }
 
 int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
-	struct sockaddr_storage *p)
+		  struct sockaddr_storage __user *p)
 {
 	int err, i, count, copycount;
 	const struct in6_addr *group;