fuzz/libelf: exit with fuzzer function return value

Now the function can return nonzero value. Use that value as exit code
for the stub program. AFL might be able to use such information to
optimise fuzzing process.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>

tools/fuzz/libelf/afl-libelf-fuzzer.c

@@ -42,9 +42,7 @@ int main(int argc, char **argv)
 
     fclose(fp);
 
-    LLVMFuzzerTestOneInput(input, size);
-
-    return 0;
+    return LLVMFuzzerTestOneInput(input, size);
 }
 
 /*