MAINTAINERS, SLAB: add Roman as reviewer, git tree

The slab code has an overlap with kmem accounting, where Roman has done
a lot of work recently and it would be useful to make sure he's CC'd on
patches that potentially affect it.  Thus add him as a reviewer for the
SLAB subsystem.

Also while at it, add the link to slab git tree.

Link: https://lkml.kernel.org/r/20220222103104.13241-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: tehcaster

MAINTAINERS

@@ -17762,8 +17762,10 @@ M:	David Rientjes <rientjes@google.com>
 M:	Joonsoo Kim <iamjoonsoo.kim@lge.com>
 M:	Andrew Morton <akpm@linux-foundation.org>
 M:	Vlastimil Babka <vbabka@suse.cz>
+R:	Roman Gushchin <roman.gushchin@linux.dev>
 L:	linux-mm@kvack.org
 S:	Maintained
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git
 F:	include/linux/sl?b*.h
 F:	mm/sl?b*