cxl/pci: Refactor cxl_hdm_decode_init()

With the previous refactoring of DVSEC range registers out of
cxl_hdm_decode_init(), it basically becomes a skeleton function. Squash
__cxl_hdm_decode_init() with cxl_hdm_decode_init() to simplify the code.
cxl_hdm_decode_init() now returns more error codes than just -EBUSY.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/167640367916.935665.12898404758336059003.stgit@dwillia2-xfh.jf.intel.com


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