aries | p1: zram: avoid null access when fail to alloc meta

zram_meta_alloc could fail so caller should check it.  Otherwise, your
system will hang.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Humberto Borba <humberos@gmail.com>

Change-Id: I216eb5f82fff0bf9158f47d5d1620dfa7ff770dd