qed: Fix potential memory corruption

A stuck ramrod should be deleted from the completion_pending list,
otherwise it will be added again in the future and corrupt the list.

Return error value to inform that ramrod is stuck and should be deleted.

Signed-off-by: Sagiv Ozeri <sagiv.ozeri@cavium.com>
Signed-off-by: Denis Bolotin <denis.bolotin@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>