cxl/region: Fix passthrough-decoder detection

A passthrough decoder is a decoder that maps only 1 target. It is a
special case because it does not impose any constraints on the
interleave-math as compared to a decoder with multiple targets. Extend
the passthrough case to multi-target-capable decoders that only have one
target selected. I.e. the current code was only considering passthrough
*ports* which are only a subset of the potential passthrough decoder
scenarios.

Fixes: e4f6dfa ("cxl/region: Fix 'distance' calculation with passthrough ports")
Cc: <stable@vger.kernel.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/167564540422.847146.13816934143225777888.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/region.c

@@ -993,10 +993,10 @@ static int cxl_port_setup_targets(struct cxl_port *port,
 		int i, distance;
 
 		/*
-		 * Passthrough ports impose no distance requirements between
+		 * Passthrough decoders impose no distance requirements between
 		 * peers
 		 */
-		if (port->nr_dports == 1)
+		if (cxl_rr->nr_targets == 1)
 			distance = 0;
 		else
 			distance = p->nr_targets / cxl_rr->nr_targets;