cxl/pmem: Fix reference counting for delayed work

cxl/pmem: Fix reference counting for delayed work

There is a potential race between queue_work() returning and the
queued-work running that could result in put_device() running before
get_device(). Introduce the cxl_nvdimm_bridge_state_work() helper that
takes the reference unconditionally, but drops it if no new work was
queued, to keep the references balanced.

Fixes: 8fdcb1704f61 ("cxl/pmem: Add initial infrastructure for pmem support")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>
Link: https://lore.kernel.org/r/163553734757.2509761.3305231863616785470.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>