n_tty: Rename tail to old_tail in n_tty_read()

The local tail variable in n_tty_read() is used for one purpose, it
keeps the old tail. Thus, rename it appropriately to improve code
readability.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/22b37499-ff9a-7fc1-f6e0-58411328d122@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -2130,7 +2130,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
 	ssize_t retval = 0;
 	long timeout;
 	bool packet;
-	size_t tail;
+	size_t old_tail;
 
 	/*
 	 * Is this a continuation of a read started earler?
@@ -2193,7 +2193,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
 	}
 
 	packet = tty->ctrl.packet;
-	tail = ldata->read_tail;
+	old_tail = ldata->read_tail;
 
 	add_wait_queue(&tty->read_wait, &wait);
 	while (nr) {
@@ -2282,7 +2282,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
 		if (time)
 			timeout = time;
 	}
-	if (tail != ldata->read_tail)
+	if (old_tail != ldata->read_tail)
 		n_tty_kick_worker(tty);
 	up_read(&tty->termios_rwsem);