cnic: Add missing error checking for RAMROD_CMD_ID_CLOSE

Completion status field should also be checked for non-zero error
condition.

Signed-off-by: Eddie Wai <eddie.wai@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>