MTR memory allocation do not depend on allocation of mtt.

This patch moves the allocation of mtr before mtt in preparation for
the following optimization.
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://lore.kernel.org/r/20240113085935.2838701-4-huangjunxian6@hisilicon.comSigned-off-by: Leon Romanovsky <leon@kernel.org>