[bpf-next v4 3/3] samples/bpf: fix uninitialized warning with test_current_task_under_cgroup

["Daniel T. Lee" <danieltimlee@gmail.com>]

Currently, compiling samples/bpf with LLVM warns about the uninitialized
use of variable with test_current_task_under_cgroup.

    ./samples/bpf/test_current_task_under_cgroup_user.c:57:6:
    warning: variable 'cg2' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
	    if (setup_cgroup_environment())
		^~~~~~~~~~~~~~~~~~~~~~~~~~
    ./samples/bpf/test_current_task_under_cgroup_user.c:106:8:
    note: uninitialized use occurs here
	    close(cg2);
		  ^~~
    ./samples/bpf/test_current_task_under_cgroup_user.c:57:2:
    note: remove the 'if' if its condition is always false
	    if (setup_cgroup_environment())
	    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./samples/bpf/test_current_task_under_cgroup_user.c:19:9:
    note: initialize the variable 'cg2' to silence this warning
	    int cg2, idx = 0, rc = 1;
		   ^
		    = 0
    1 warning generated.

This commit resolve this compiler warning by pre-initialize the variable
with error for safeguard.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
---
 samples/bpf/test_current_task_under_cgroup_user.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/samples/bpf/test_current_task_under_cgroup_user.c b/samples/bpf/test_current_task_under_cgroup_user.c
index ac251a417f45..6fb25906835e 100644
--- a/samples/bpf/test_current_task_under_cgroup_user.c
+++ b/samples/bpf/test_current_task_under_cgroup_user.c
@@ -14,9 +14,9 @@
 int main(int argc, char **argv)
 {
 	pid_t remote_pid, local_pid = getpid();
+	int cg2 = -1, idx = 0, rc = 1;
 	struct bpf_link *link = NULL;
 	struct bpf_program *prog;
-	int cg2, idx = 0, rc = 1;
 	struct bpf_object *obj;
 	char filename[256];
 	int map_fd[2];
@@ -103,7 +103,9 @@ int main(int argc, char **argv)
 	rc = 0;
 
 err:
-	close(cg2);
+	if (cg2 != -1)
+		close(cg2);
+
 	cleanup_cgroup_environment();
 
 cleanup:
-- 
2.34.1