MAINTAINERS: add hugetlb_cgroup.c to hugetlb section

This file is clearly specific to hugetlb so this seems the most
appropriate place for it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Lorenzo Stoakes <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Oscar Salvador <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: lorenzo-stoakes

MAINTAINERS

@@ -11169,6 +11169,7 @@ F:	fs/hugetlbfs/
 F:	include/linux/hugetlb.h
 F:	include/trace/events/hugetlbfs.h
 F:	mm/hugetlb.c
+F:	mm/hugetlb_cgroup.c
 F:	mm/hugetlb_cma.c
 F:	mm/hugetlb_cma.h
 F:	mm/hugetlb_vmemmap.c