IB/mlx5: Return error for unsupported signature type

IB/mlx5: Return error for unsupported signature type

In case of unsupported singature, we returned positive
value, while the better approach is to return -EINVAL.

In addition, in this change, the error print is enriched
to provide an actual supplied signature type.

Fixes: e6631814fb3a ("IB/mlx5: Support IB_WR_REG_SIG_MR")
Cc: Sagi Grimberg <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>