Char: n_r3964, use wait_event_interruptible

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>