Fix magic number in bucket declaration

Replace the hard-coded value 256 with BUCKET_SIZE macro to improve
readability and maintainability.

Change-Id: I4b123b7267dcb9beac8d791fd1e7cb9b75a6b446

Author: ibat10clw

shannon_entropy.c

@@ -15,7 +15,7 @@ double shannon_entropy(const uint8_t *s)
     uint64_t entropy_sum = 0;
     const uint64_t entropy_max = 8 * LOG2_RET_SHIFT;
 
-    uint32_t bucket[256];
+    uint32_t bucket[BUCKET_SIZE];
     memset(&bucket, 0, sizeof(bucket));
 
     for (uint32_t i = 0; i < count; i++)