[HW] Remove defensive, unnecessary default

Remove some defensive coding that added a default case to a fully covered
switch statement.  This is a compile time warning if not removed.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

lib/CAPI/Dialect/HW.cpp

@@ -143,8 +143,6 @@ void hwModuleTypeGetPort(MlirType type, intptr_t index, HWModulePort *ret) {
   case ModulePort::Direction::InOut:
     dir = HWModulePortDirection::InOut;
     break;
-  default:
-    llvm_unreachable("unknown ModulePort::Direction");
   }
 
   ret->name = wrap(static_cast<Attribute>(port.name));