staging/fwserial: Remove reference to removed constant

FWSERIAL_TTY_START_MINOR was removed. The minor_start is allocated
by tty_alloc_driver().
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fwserial/fwserial.h

@@ -194,7 +194,7 @@ struct buffered_rx {
  * @port: underlying tty_port
  * @device: tty device
  * @index: index into port_table for this particular port
- *    note: minor = index + FWSERIAL_TTY_START_MINOR
+ *    note: minor = index + minor_start assigned by tty_alloc_driver()
  * @serial: back pointer to the containing fw_serial
  * @rx_handler: bus address handler for unique addr region used by remotes
  *              to communicate with this port. Every port uses