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>

lib/iov_iter.c

@@ -581,7 +581,7 @@ static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
 static __wsum csum_and_memcpy(void *to, const void *from, size_t len,
 			      __wsum sum, size_t off)
 {
-	__wsum next = csum_partial_copy_nocheck(from, to, len, 0);
+	__wsum next = csum_partial_copy_nocheck(from, to, len);
 	return csum_block_add(sum, next, off);
 }