util/pingpong: Fix coverity issue about integer overflow

The calculation of `power_of_two` would overflow when `i` reaches 32.
Based on the size of allocated array `sizes`, `i` should be less than
32. Add explicit loop limit to suppress the warning.

Signed-off-by: Jianxin Xiong <jianxin.xiong@intel.com>

util/pingpong.c

@@ -982,7 +982,7 @@ static int generate_test_sizes(struct pp_opts *opts, size_t tx_size, int **sizes
 			n++;
 		}
 	} else {
-		for (i = 0;; i++) {
+		for (i = 0; i < 32; i++) {
 			power_of_two = (i == 0) ? 0 : (1 << i);
 			half_up =
 			    (i == 0) ? 1 : power_of_two + (power_of_two / 2);