tty: incorrect test of echo_buf() result for ECHO_OP_START

test echo_buf() result for ECHO_OP_START
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -767,7 +767,7 @@ static size_t __process_echoes(struct tty_struct *tty)
 	 * of echo overrun before the next commit), then discard enough
 	 * data at the tail to prevent a subsequent overrun */
 	while (ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
-		if (echo_buf(ldata, tail == ECHO_OP_START)) {
+		if (echo_buf(ldata, tail) == ECHO_OP_START) {
 			if (echo_buf(ldata, tail) == ECHO_OP_ERASE_TAB)
 				tail += 3;
 			else