ksmbd: fix passing freed memory 'aux_payload_buf'

[ Upstream commit 59d8d24f4610333560cf2e8fe3f44cafe30322eb ]

The patch e2b76ab8b5c9: "ksmbd: add support for read compound" leads
to the following Smatch static checker warning:

  fs/smb/server/smb2pdu.c:6329 smb2_read()
        warn: passing freed memory 'aux_payload_buf'

It doesn't matter that we're passing a freed variable because nbytes is
zero. This patch set "aux_payload_buf = NULL" to make smatch silence.

Fixes: e2b76ab8b5c9 ("ksmbd: add support for read compound")
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

fs/ksmbd/smb2pdu.c

@@ -6314,7 +6314,7 @@ int smb2_read(struct ksmbd_work *work)
 						      aux_payload_buf,
 						      nbytes);
 		kvfree(aux_payload_buf);
-
+		aux_payload_buf = NULL;
 		nbytes = 0;
 		if (remain_bytes < 0) {
 			err = (int)remain_bytes;