MAINTAINERS: add Sergey as zsmalloc reviewer

Nominate myself as a zsmalloc reviewer.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -11674,6 +11674,7 @@ F:	drivers/tty/serial/zs.*
 ZSMALLOC COMPRESSED SLAB MEMORY ALLOCATOR
 M:	Minchan Kim <minchan@kernel.org>
 M:	Nitin Gupta <ngupta@vflare.org>
+R:	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
 L:	linux-mm@kvack.org
 S:	Maintained
 F:	mm/zsmalloc.c