can: avoids a false warning

At this point optlen == sizeof(sfilter) but some compilers are dumb.

Reported-by: Németh Márton <nm127@freemail.h
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/can/raw.c

@@ -445,7 +445,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 				return -EFAULT;
 			}
 		} else if (count == 1) {
-			if (copy_from_user(&sfilter, optval, optlen))
+			if (copy_from_user(&sfilter, optval, sizeof(sfilter)))
 				return -EFAULT;
 		}