dax: remove the pgmap sanity checks in generic_fsdax_supported

dax: remove the pgmap sanity checks in generic_fsdax_supported

Drivers that register a dax_dev should make sure it works, no need
to double check from the file system.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20211129102203.2243509-6-hch@lst.de
Signed-off-by: Dan Williams <dan.j.williams@intel.com>