uml: fix helper_wait calls in watchdog

In commit 1aa351a3

 ("uml: tidy helper
code") the arguments of helper_wait() were changed.  The adaptation of
harddog_user.c was forgotten, so this errors occur:

  /arch/um/drivers/harddog_user.c: In function 'start_watchdog':
  /arch/um/drivers/harddog_user.c:82: error: too many arguments to function 'helper_wait'
  /arch/um/drivers/harddog_user.c:89: error: too many arguments to function 'helper_wait'

Signed-off-by: Johann Felix Soden <johfel@users.sourceforge.net>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>