qed: Fix possible race when reading firmware return code.

While handling SPQ ramrod completion, there is a possible race
where driver might not read updated fw return code based on
ramrod completion done. This patch ensures that fw return code
is written first and then completion done flag is updated
using appropriate memory barriers.

Signed-off-by: Manish Chopra <manish.chopra@caviumnetworks.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@caviumnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>