tty: introduce wait_event_interruptible_tty

Calling wait_event_interruptible implicitly
releases the BKL when it sleeps, but we need
to do this explcitly when we have converted
it to a mutex.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/n_r3964.c b/drivers/char/n_r3964.c
index f4bd259..a98290d 100644
--- a/drivers/char/n_r3964.c
+++ b/drivers/char/n_r3964.c
@@ -1079,7 +1079,7 @@
 				goto unlock;
 			}
 			/* block until there is a message: */
-			wait_event_interruptible(pInfo->read_wait,
+			wait_event_interruptible_tty(pInfo->read_wait,
 					(pMsg = remove_msg(pInfo, pClient)));
 		}