RADIO: Add an explicit check to silence a build warning

clang did not like that in this function it looks like
it may return an unitialized value, even though
it should not happen, let's add a runtime else with an
error. Both to silence the build warning and error out
in runtime if it ever happens.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

src/HW_models/NHW_RADIO_utils.c

@@ -273,6 +273,8 @@ static p2G4_modulation_t nhra_modulation_from_mode(uint32_t MODE) {
   } else if ((MODE == RADIO_MODE_MODE_Ble_LR125Kbit)
              || (MODE == RADIO_MODE_MODE_Ble_LR500Kbit)) {
     modulation = P2G4_MOD_BLE_CODED;
+  } else {
+    bs_trace_error_time_line("programming error: Unsupported MODE %u\n", MODE);
   }
   return modulation;
 }