scsi: qla2xxx: Return switch command on a timeout

This patch fixes commit bcc71cc3 ("scsi: qla2xxx: Fix for double
free of SRB structure") which placed code in wrong routines.

Also updated the use of WARN_ON() to WARN_ON_ONCE() to prevent
flooding log messages.

Fixes: bcc71cc3 ("scsi: qla2xxx: Fix for double free of SRB structure")
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>