tools/crypto_bench: check malloc fail before using it

Need to check malloc fail before using it, so adjust the location
in the code.
Reviewed-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>

tools/crypto_bench.c

@@ -665,8 +665,8 @@ struct hash_impl implementations[] = {
 
 int main(int argc, char **argv)
 {
-    uint8_t *input = av_malloc(MAX_INPUT_SIZE * 2);
-    uint8_t *output = input + MAX_INPUT_SIZE;
+    uint8_t *input;
+    uint8_t *output;
     unsigned i, impl, size;
     int opt;
 
@@ -702,12 +702,14 @@ int main(int argc, char **argv)
             exit(opt != 'h');
         }
     }
-
+    input = av_malloc(MAX_INPUT_SIZE * 2);
     if (!input)
         fatal_error("out of memory");
     for (i = 0; i < MAX_INPUT_SIZE; i += 4)
         AV_WB32(input + i, i);
 
+    output = input + MAX_INPUT_SIZE;
+
     size = MAX_INPUT_SIZE;
     for (impl = 0; impl < FF_ARRAY_ELEMS(implementations); impl++)
         run_implementation(input, output, &implementations[impl], size);