dax: fix missing-prototype warnings

dax: fix missing-prototype warnings

dev_dax_probe declaration for this function was removed with the only
caller outside of device.c. Mark it static to avoid a W=1
warning:
drivers/dax/device.c:399:5: error: no previous prototype for 'dev_dax_probe'

Similarly, run_dax() causes a warning, but this one is because the
declaration needs to be included:

drivers/dax/super.c:337:6: error: no previous prototype for 'run_dax'

Fixes: 83762cb5c7c4 ("dax: Kill DEV_DAX_PMEM_COMPAT")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230517125532.931157-1-arnd@kernel.org
Signed-off-by: Dan Williams <dan.j.williams@intel.com>