apparmor: fix missing error check for rhashtable_insert_fast

 rhashtable_insert_fast() could return err value when memory allocation is
 failed. but unpack_profile() do not check values and this always returns
 success value. This patch just adds error check code.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: e025be0f26d5 ("apparmor: support querying extended trusted helper extra data")

Signed-off-by: Danila Chernetsov <listdansp@mail.ru>
Signed-off-by: John Johansen <john.johansen@canonical.com>