mlx5_core: Simplify signature handover wqe for interleaved buffers

No need for repetition format pattern in case the data and protection
are already interleaved in the memory domain since the pattern
already exists. A single key entry is sufficient and may save some
extra fetch ops.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>