ratecontrol: Use correct function pointer casts instead of void*

libavcodec/ratecontrol.c:120:9: warning: ISO C forbids initialization between function pointer and ‘void *’ [-Wpedantic]
libavcodec/ratecontrol.c:121:9: warning: ISO C forbids initialization between function pointer and ‘void *’ [-Wpedantic]

libavcodec/ratecontrol.c

@@ -472,8 +472,8 @@ av_cold int ff_rate_control_init(MpegEncContext *s)
         NULL
     };
     static double (* const func1[])(void *, double) = {
-        (void *)bits2qp,
-        (void *)qp2bits,
+        (double (*)(void *, double)) bits2qp,
+        (double (*)(void *, double)) qp2bits,
         NULL
     };
     static const char * const func1_names[] = {