zram: add Designated Reviewer for zram in MAINTAINERS

Sergey Senozhatsky has contributed/reviewed to zram for a long time.  He
is really helpful for maintaining zram so I want for him to continue
helping me as Designated Reviewer unless he hates it.
Signed-off-by: NMinchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -11037,6 +11037,7 @@ F:	drivers/media/pci/zoran/
 ZRAM COMPRESSED RAM BLOCK DEVICE DRVIER
 M:	Minchan Kim <minchan@kernel.org>
 M:	Nitin Gupta <ngupta@vflare.org>
+R:	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
 L:	linux-kernel@vger.kernel.org
 S:	Maintained
 F:	drivers/block/zram/