mxser: clean up timeout handling in mxser_wait_until_sent()

timeout cannot be zero at the point of use. So no need to check for
zero. Also precompute the expiration time (into expire) and use it. This
makes the code more clear.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20211118073125.12283-14-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/mxser.c

@@ -1420,15 +1420,14 @@ static bool mxser_tx_empty(struct mxser_port *info)
 static void mxser_wait_until_sent(struct tty_struct *tty, int timeout)
 {
 	struct mxser_port *info = tty->driver_data;
-	unsigned long orig_jiffies, char_time;
+	unsigned long expire, char_time;
 
 	if (info->type == PORT_UNKNOWN)
 		return;
 
 	if (info->xmit_fifo_size == 0)
 		return;		/* Just in case.... */
 
-	orig_jiffies = jiffies;
 	/*
 	 * Set the check interval to be 1/5 of the estimated time to
 	 * send a single character, and make it at least 1.  The check
@@ -1458,11 +1457,13 @@ static void mxser_wait_until_sent(struct tty_struct *tty, int timeout)
 	if (!timeout || timeout > 2 * info->timeout)
 		timeout = 2 * info->timeout;
 
+	expire = jiffies + timeout;
+
 	while (mxser_tx_empty(info)) {
 		msleep_interruptible(char_time);
 		if (signal_pending(current))
 			break;
-		if (timeout && time_after(jiffies, orig_jiffies + timeout))
+		if (time_after(jiffies, expire))
 			break;
 	}
 }