cxl/region: Stop initializing interleave granularity

In preparation for a patch that validates that the region ways setting
is compatible with the granularity setting, the initial granularity
setting needs to start at zero to indicate "unset".

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://lore.kernel.org/r/165853777484.2430596.3423921169034844397.stgit@dwillia2-xfh.jf.intel.com
[djbw: fix up unused variable]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>