dax: simplify dax_synchronous and set_dax_synchronous

Remove the pointless wrappers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/20211215084508.435401-3-hch@lst.de


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