gr-filter: cpp code genration fails for root raised cosine filter

The rrc block has no parameter type.fcn, which is wrongly  used in cpp code generation
but not in python code generation.

Signed-off-by: Volker Schroer <3470424+dl1ksv@users.noreply.github.com>

gr-filter/grc/filter_root_raised_cosine_filter.block.yml

@@ -75,7 +75,7 @@ cpp_templates:
     make: |-
         this->${id} = filter::${type}::make(
             ${ interp if str(type).startswith('interp') else decim },
-            firdes.${type.fcn}(
+            firdes::root_raised_cosine(
                 ${gain},
                 ${samp_rate},
                 ${sym_rate},