UPSTREAM: zram: clean up zram_meta_alloc()

(cherry-pick from commit b8179958327a1f513efca095ba782a1986c7c4fb)

A trivial cleanup of zram_meta_alloc() error handling.

Bug: 25951511

Change-Id: I73b05e63dc4580191fc50857af0e4f37b56c0f05
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>