RDMA/bnxt_re: Fix return value of poll routine

Fix the incorrect reporting of number of polled
entries by taking into account the max CQ depth
in the driver.

Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>