Not all zero page implementations use empty_zero_page global pointer so
let's substitute empty_zero_page occurence with helper ZERO_PAGE(0).
Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Link: https://lore.kernel.org/r/20221018215755.33566-2-giulio.benetti@benettiengineering.comSigned-off-by: Mark Brown <broonie@kernel.org>