vdpa/mlx5: fix completion queue arming

vdpa/mlx5: fix completion queue arming

The mlx5 vDPA driver manages QP and CQ in order to forward the HW event
to the guest by the callfd file descriptor for each virtq.

The driver arms the CQ for the next CQE index that should be
completed by the HW in order to create completion event.

In the SW completion event handler, the driver arms the CQ again for the
next index,

The CQE index in the CQ doorbell and in the CQ doorbell record was
masked incorrectly with the CQ size mask while it should be masked only
with 0xFFFFFF mask.

Remove the CQ size mask, stay only with 0xFFFFFF mask.

Fixes: 8395927cdfaf ("vdpa/mlx5: prepare HW queues")

Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>