Replace the remaining espeak_ERROR code usage with espeak_ng_STATUS.

src/include/espeak-ng/espeak_ng.h

 	ENS_MBROLA_NOT_FOUND         = 0x100007FF,
 	ENS_MBROLA_VOICE_NOT_FOUND   = 0x100008FF,
 	ENS_EVENT_BUFFER_FULL        = 0x100009FF,
+	ENS_NOT_SUPPORTED            = 0x10000AFF,
 } espeak_ng_STATUS;
 
 typedef enum {

src/libespeak-ng/speech.c

 	t_espeak_command *c = create_espeak_parameter(parameter, value, relative);
 
 	espeak_ng_STATUS status = fifo_add_command(c);
-	if (status != EE_OK)
+	if (status != ENS_OK)
 		delete_espeak_command(c);
 	return status;
 #else

src/libespeak-ng/synth_mbrola.c

 
 // mbrola interface is not compiled, provide dummy functions.
 
-espeak_ERROR LoadMbrolaTable(const char *mbrola_voice, const char *phtrans, int *srate)
+espeak_ng_STATUS LoadMbrolaTable(const char *mbrola_voice, const char *phtrans, int *srate)
 {
-	return EE_INTERNAL_ERROR;
+	return ENS_NOT_SUPPORTED;
 }
 
 int MbrolaGenerate(PHONEME_LIST *phoneme_list, int *n_ph, int resume)

src/libespeak-ng/voices.c

 			DoVoiceChange(voice);
 			voice_selector.languages = voice->language_name;
 			SetVoiceStack(&voice_selector, variant_name);
-			return EE_OK;
+			return ENS_OK;
 		}
 	}
 	return ENS_VOICE_NOT_FOUND;