USB: serial: mos7840: drop buffer-callback return-value comments

The driver write_room and chars_in_buffer callbacks used to incorrectly
return a negative errno in case they were called with a NULL port
driver-data pointer or if some other always-true sanity checks failed.

The bogus sanity checks were later removed by commit ce039bd4 ("USB:
serial: mos7840: drop paranoid port checks") and 7b2faede ("USB:
serial: mos7840: drop port driver data accessors") but the
function-header comments were never updated to match.

Drop the outdated return-value comments.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/mos7840.c

@@ -730,9 +730,6 @@ static int mos7840_open(struct tty_struct *tty, struct usb_serial_port *port)
  *	this function is called by the tty driver when it wants to know how many
  *	bytes of data we currently have outstanding in the port (data that has
  *	been written, but hasn't made it out the port yet)
- *	If successful, we return the number of bytes left to be written in the
- *	system,
- *	Otherwise we return zero.
  *****************************************************************************/
 
 static unsigned int mos7840_chars_in_buffer(struct tty_struct *tty)
@@ -814,8 +811,6 @@ static void mos7840_break(struct tty_struct *tty, int break_state)
  * mos7840_write_room
  *	this function is called by the tty driver when it wants to know how many
  *	bytes of data we can accept for a specific port.
- *	If successful, we return the amount of room that we have for this port
- *	Otherwise we return a negative error number.
  *****************************************************************************/
 
 static unsigned int mos7840_write_room(struct tty_struct *tty)