mm/page_alloc: correct the wrong cpuset file path in comment

cpuset.c was moved to kernel/cgroup/ in below commit
201af4c0fab0 ("cgroup: move cgroup files under kernel/cgroup/")
Correct the wrong path in comment.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Mark-PK Tsai <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/page_alloc.c

···
 retry:
 	/*
 	 * Scan zonelist, looking for a zone with enough free.
-	 * See also __cpuset_node_allowed() comment in kernel/cpuset.c.
+	 * See also __cpuset_node_allowed() comment in kernel/cgroup/cpuset.c.
 	 */
 	no_fallback = alloc_flags & ALLOC_NOFRAGMENT;
 	z = ac->preferred_zoneref;