net/9p: switch to copy_from_iter_full()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index 16d2875..16e1068 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -74,7 +74,7 @@ pdu_write_u(struct p9_fcall *pdu, struct iov_iter *from, size_t size)
 {
 	size_t len = min(pdu->capacity - pdu->size, size);
 	struct iov_iter i = *from;
-	if (copy_from_iter(&pdu->sdata[pdu->size], len, &i) != len)
+	if (!copy_from_iter_full(&pdu->sdata[pdu->size], len, &i))
 		len = 0;
 
 	pdu->size += len;