obs-ffmpeg: Fix NVENC "mq" to use P6 rather than P4

plugins/obs-ffmpeg/jim-nvenc.c

@@ -468,7 +468,7 @@ static bool init_encoder_base(struct nvenc_data *enc, obs_data_t *settings,
 			nv_multipass = NV_ENC_TWO_PASS_QUARTER_RESOLUTION;
 
 		} else if (astrcmpi(preset, "mq") == 0) {
-			nv_preset = NV_ENC_PRESET_P4_GUID;
+			nv_preset = NV_ENC_PRESET_P6_GUID;
 			nv_tuning = NV_ENC_TUNING_INFO_HIGH_QUALITY;
 			nv_multipass = NV_ENC_TWO_PASS_QUARTER_RESOLUTION;