commit 6df200f5 upstream.

Return the NULL pointer when the allocation fails.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>