csum_partial_copy_nocheck(): drop the last argument

It's always 0.  Note that we theoretically could use ~0U as well -
result will be the same modulo 0xffff, _if_ the damn thing did the
right thing for any value of initial sum; later we'll make use of
that when convenient.

However, unlike csum_and_copy_..._user(), there are instances that
did not work for arbitrary initial sums; c6x is one such.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

net/ipv4/raw.c

@@ -478,7 +478,7 @@ static int raw_getfrag(void *from, char *to, int offset, int len, int odd,
 			skb->csum = csum_block_add(
 				skb->csum,
 				csum_partial_copy_nocheck(rfv->hdr.c + offset,
-							  to, copy, 0),
+							  to, copy),
 				odd);
 
 		odd = 0;