runc update: don't lose intelRdt state

Prevent --l3-cache-schema from clearing the intel_rdt.memBwSchema state
and --mem-bw-schema clearing l3_cache_schema, respectively.

Signed-off-by: Markus Lehtonen <markus.lehtonen@intel.com>

update.go

@@ -387,9 +387,13 @@ other options are ignored.
 					return err
 				}
 			}
+			if l3CacheSchema != "" {
 				config.IntelRdt.L3CacheSchema = l3CacheSchema
+			}
+			if memBwSchema != "" {
 				config.IntelRdt.MemBwSchema = memBwSchema
 			}
+		}
 
 		// XXX(kolyshkin@): currently "runc update" is unable to change
 		// device configuration, so add this to skip device update.