filter-graph: add latency option to the convolver

Sometimes you want to use the convolver as a delay without adding
latency so add a latency option to tweak the automatic latency
reporting. Use this in the upmix rear delay filters.

src/daemon/filter-chain/sink-upmix-5.1-filter.conf

@@ -87,6 +87,7 @@ context.modules = [
 			    delay = 0.012
                             filename = "/hilbert"
 			    length = 33
+			    latency = 0.0
 			}
 		    }
                     {
@@ -101,6 +102,7 @@ context.modules = [
 			    delay = 0.012
                             filename = "/hilbert"
 			    length = 33
+			    latency = 0.0
 			}
 		    }
                  ]