[SCSI] qla2xxx: Acquire hardware lock while manipulating dsd list.

The dsd list shouldn't be manipulated without taking the per host hardware
lock to prevent multiple callers from trampling upon one another.

Signed-off-by: Saurav Kashyap <saurav.kashyap@qlogic.com>
Signed-off-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>