tests: utils_test: Fix test failure when compiling with -O0

It seems with default flags in_buf was being memzeroed by the compiler.
When compiling with -O0, that's not the case anymore and printf prints
after first 16 bytes, printing extra garbage which doesn't match the
expected output.

Change-Id: I736c1e4d625f647d3bb794fa717256e9dbf36e87

tests/utils/utils_test.c

@@ -334,6 +334,7 @@ static void str_escape_test(void)
 
 	printf("\nTesting string escaping\n");
 	printf("- all chars from 0 to 255 in batches of 16:\n");
+	in_buf[16] = '\0';
 	for (j = 0; j < 16; j++) {
 		for (i = 0; i < 16; i++)
 			in_buf[i] = (j << 4) | i;