samples/bpf: test_cgrp2_sock2: fix an off by one

"prog_cnt" is the number of elements which are filled out in prog_fd[]
so the test should be >= instead of >.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

samples/bpf/test_cgrp2_sock2.c

@@ -51,7 +51,7 @@ int main(int argc, char **argv)
 	if (argc > 3)
 		filter_id = atoi(argv[3]);
 
-	if (filter_id > prog_cnt) {
+	if (filter_id >= prog_cnt) {
 		printf("Invalid program id; program not found in file\n");
 		return EXIT_FAILURE;
 	}