RDMA/erdma: Renaming variable names and field names of struct erdma_mem

Currently, variable names and field names of struct erdma_mem contain
'mtt', which is not accurate. Renaming them with 'xxx_mem' or 'mem'.

Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230817102151.75964-2-chengyou@linux.alibaba.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>