scsi: qla2xxx: Add retry limit for fabric scan logic

Switch scan is assumed to succeed most of the time.
If the scan failed, then scan is limit 5 retries.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>