cxl/hdm: Use local hdm variable

Save a few characters and use the already initialized local variable.

Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Adam Manzanares <a.manzanares@samsung.com>
Link: https://lore.kernel.org/r/165603872171.551046.913207574344536475.stgit@dwillia2-xfh


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