The nfit_device_lock() helper was added to provide lockdep coverage for
the NFIT driver's usage of device_lock() on the nvdimm_bus object. Now
that nvdimm_bus objects have their own lock class this wrapper can be
dropped.

Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/165055521409.3745911.8085645201146909612.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>