obs-filters: Fix building without noise reduction

plugins/obs-filters/CMakeLists.txt

@@ -43,6 +43,8 @@ else()
 		set(obs-filters_NOISEREDUCTION_LIBRARIES
 			${LIBSPEEXDSP_LIBRARIES} ${LIBRNNOISE_LIBRARIES})
 		set(NOISEREDUCTION_ENABLED TRUE)
+	else()
+		set(NOISEREDUCTION_ENABLED FALSE)
 	endif()
 endif()