qed: Fix setting/clearing bit in completion bitmap

Slowpath completion handling is incorrectly changing
SPQ_RING_SIZE bits instead of a single one.

Fixes: 76a9a364 ("qed: fix handling of concurrent ramrods")
Signed-off-by: Manish Chopra <manish.chopra@qlogic.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>