qed: fix assignment of n_rq_elems to incorrect params field

Currently n_rq_elems is being assigned to params.elem_size instead of the
field params.num_elems.  Coverity is detecting this as a double assingment
to params.elem_size and reporting this as an usused value on the first
assignment.  Fix this.

Addresses-Coverity: ("Unused value")
Fixes: b6db3f71 ("qed: simplify chain allocation with init params struct")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>