FASTMODEL: update trng based on comments

Author: Qinghao Shi

targets/TARGET_ARM_FM/TARGET_FVP_MPS2/trng_api.c

@@ -44,13 +44,11 @@ void trng_free(trng_t *obj)
 int trng_get_bytes(trng_t *obj, uint8_t *output, size_t length, size_t *output_length)
 {
     (void)obj;
-    (void)output;
 
     for (int i = 0; i < length; ++i) {
         output[i] = rand() % 256;
     }
     *output_length = length;
 
     return 0;
-
 }