staging: lustre: Fix sparse warning for one-bit signed bitfield

Fix the following sparse warning:
drivers/staging/lustre/lustre/llite/llite_internal.h:461:49: error:dubious one-bit signed bitfield

Signed-off-by: Dulshani Gunawardhana <dulshani.gunawardhana89@gmail.com>
Reviewed-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>