BuildHuffmanTable: clear int sanitizer warning

clears a warning of the form:
implicit conversion from type 'int' of value -1 (32-bit, signed) to type
'uint32_t' (aka 'unsigned int') changed the value to 4294967295 (32-bit,
unsigned)

Bug: b/229626362
Change-Id: I397fbd59bd3e6d787fcec1344b6230958b28d22c

src/utils/huffman_utils.c

@@ -142,7 +142,7 @@ static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
 
   {
     int step;              // step size to replicate values in current table
-    uint32_t low = -1;     // low bits for current root entry
+    uint32_t low = 0xffffffffu;        // low bits for current root entry
     uint32_t mask = total_size - 1;    // mask for low bits
     uint32_t key = 0;      // reversed prefix code
     int num_nodes = 1;     // number of Huffman tree nodes