smb: client: fix uninitialized variable in smb2_writev_callback

compiling with W=2 pointed out that "written may be used uninitialized"

Fixes: 20d72b0 ("netfs: Fix the request's work item to not require a ref")
Cc: stable@vger.kernel.org
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: smfrench

fs/smb/client/smb2pdu.c

@@ -4955,7 +4955,7 @@ smb2_writev_callback(struct TCP_Server_Info *server, struct mid_q_entry *mid)
 	unsigned int rreq_debug_id = wdata->rreq->debug_id;
 	unsigned int subreq_debug_index = wdata->subreq.debug_index;
 	ssize_t result = 0;
-	size_t written;
+	size_t written = 0;
 
 	WARN_ONCE(wdata->server != server,
 		  "wdata server %p != mid server %p",