added license info

fftw.c

+/*
+ * =====================================================================================
+ *
+ *       Filename:  fftw.c
+ *
+ *    Description:  FFTW profiling
+ *
+ *        Version:  1.0
+ *        Created:  29.01.2021 10:55:14
+ *       Revision:  none
+ *       Compiler:  gcc
+ *
+ *         Author:  Henning Fehrmann (), henning.fehrmann@aei.mpg.de
+ *   Organization:  AEI Hannover
+ *        License:  GNU General Public License v2
+ *
+ * =====================================================================================
+ */
+
+
 #define __HIP_PLATFORM_HCC__
 
 #include <stdio.h>