pmem: refactor pmem_clear_poison()

Refactor the pmem_clear_poison() function such that the common
shared code between the typical write path and the recovery write
path is factored out.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jane Chu <jane.chu@oracle.com>
Link: https://lore.kernel.org/r/20220422224508.440670-7-jane.chu@oracle.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>