[SCSI] qla2xxx: Fix for locking issue between driver ISR and mailbox routines

The driver uses ha->mbx_cmd_flags variable to pass information between
its ISR and mailbox routines, however, it does so without the protection of
any locks.  Under certain conditions, this can lead to multiple mailbox
command completions being signaled, which, in turn, leads to a false
mailbox timeout error for the subsequently issued mailbox command.

The issue occurs frequently but intermittenly with the Qlogic 8GFC mezz
card during card initialization, resulting in card initialization failure.

Signed-off-by: Gurinder (Sunny) Shergill <gurinder.shergill@hp.com>
Acked-by: Saurav Kashyap <saurav.kashyap@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>