tty/serial/mux.c: linux/tty.h included twice

drivers/tty/serial/mux.c included 'linux/tty.h' twice, remove
the duplicate.
Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/mux.c

@@ -17,7 +17,6 @@
 */
 
 #include <linux/module.h>
-#include <linux/tty.h>
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/serial.h>