Amiga serial driver: port_write_mutex fixup

The port_write_mutex was converted from a semaphore to a mutex,
but there was still this ifdef'd init_MUTEX reference remaining.

Signed-off-by: Daniel Walker <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/ser_a2232.c

···
 		port->gs.closing_wait = 30 * HZ;
 		port->gs.rd = &a2232_real_driver;
 #ifdef NEW_WRITE_LOCKING
-		init_MUTEX(&(port->gs.port_write_mutex));
+		mutex_init(&(port->gs.port_write_mutex));
 #endif
 		init_waitqueue_head(&port->gs.open_wait);
 		init_waitqueue_head(&port->gs.close_wait);