Comment why we add INSTANCE_PATH specifically for SMPGROUP

Change-Id: Iece3678f64ef623464144b3f6a189d0516e01564
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/59313
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Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>

src/usr/targeting/common/Targets.pm

@@ -1121,6 +1121,8 @@ sub setCommonAttrForChiplet
     }
     elsif ($tgt_type eq "SMPGROUP")
     {
+        # SMPGROUP inherits the same INSTANCE_PATH as its parent OBUS which
+        # messes up the HUID -NID mapping, hence adding the below line
         $self->setAttribute($target, "INSTANCE_PATH", $target);
         $unit_pos = $pos%2;
     }