fix exit_program() prototypes

This fixes 2 warnings
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -378,7 +378,7 @@ static int decode_interrupt_cb(void *ctx)
 
 const AVIOInterruptCB int_cb = { decode_interrupt_cb, NULL };
 
-static void exit_program()
+static void exit_program(void)
 {
     int i, j;
 

ffprobe.c

@@ -141,7 +141,7 @@ static const char unit_bit_per_second_str[] = "bit/s";
 static uint64_t *nb_streams_packets;
 static uint64_t *nb_streams_frames;
 
-static void exit_program()
+static void exit_program(void)
 {
     av_dict_free(&fmt_entries_to_show);
 }