scsi: qedf: fixup compilation warning about atomic_t usage

Based on an original patch by Hannes Reinecke.

The driver didn't follow the atomic_t vs refcount_t change, and anyway
one should be using kref_read() instead of accessing the counter inside
an kref.

Fixes: 61d8658b ("scsi: qedf: Add QLogic FastLinQ offload FCoE driver framework.)
Cc: Hannes Reinecke <hare@suse.de>
Cc: Nilesh Javali <nilesh.javali@cavium.com>
Signed-off-by: Dupuis, Chad <chad.dupuis@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>