Fix missing-prototype error in programs/fuzz by moving LLVMFuzzerTestOneInput prototype to common.h

Signed-off-by: Michael Schuster <michael@schuster.ms>
diff --git a/programs/fuzz/fuzz_pubkey.c b/programs/fuzz/fuzz_pubkey.c
index 0b153b1..b2500e5 100644
--- a/programs/fuzz/fuzz_pubkey.c
+++ b/programs/fuzz/fuzz_pubkey.c
@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include "mbedtls/pk.h"
+#include "common.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
 {