Revert "cgroup: enable cgroup_get_from_file() on cgroup1"

This reverts commit f3a2aeb.

Some callers of this function depended on the fact that it only supports
cgroup v2. Revert it now, and introduce a new function in a later patch
that supports both cgroup v1 and v2, for callers that need to support
both.

Reported-by: Christian A. Ehrhardt <lk@c--e.de>
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>

kernel/cgroup/cgroup.c

@@ -6167,6 +6167,11 @@ static struct cgroup *cgroup_get_from_file(struct file *f)
 		return ERR_CAST(css);
 
 	cgrp = css->cgroup;
+	if (!cgroup_on_dfl(cgrp)) {
+		cgroup_put(cgrp);
+		return ERR_PTR(-EBADF);
+	}
+
 	return cgrp;
 }