MAINTAINERS: update maintainers for HugeTLB

Change my role to Maintainer as I am quite involved in HugeTLB
development, and will be more so with the upcoming HugetLB-pagewalk
unification, so I would like to help Munchun take care of the code. 
Besides, having two people will help in offloading some pressure.

Also add David as a Reviewer since he has quite some knowledge in the
field and has already provided valuable feedback.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Oscar Salvador <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: Muchun Song <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Peter Xu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: osalvadorvilardaga

MAINTAINERS

@@ -11157,7 +11157,8 @@ F:	include/linux/platform_data/huawei-gaokun-ec.h
 
 HUGETLB SUBSYSTEM
 M:	Muchun Song <[email protected]>
-R:	Oscar Salvador <[email protected]>
+M:	Oscar Salvador <[email protected]>
+R:	David Hildenbrand <[email protected]>
 L:	[email protected]
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-kernel-mm-hugepages