autofs4: use wait_event_killable

This playing with signals to allow only fatal signals appears to predate
the introduction of wait_event_killable(), and I'm fairly sure that
wait_event_killable is what was meant to happen here.

[avagin@openvz.org: use wake_up() instead of wake_up_interruptible]
  Link: http://lkml.kernel.org/r/20180331022839.21277-1-avagin@openvz.org
Link: http://lkml.kernel.org/r/20180319191609.23880-1-willy@infradead.org


Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Ian Kent <raven@themaw.net>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>