[SCSI] mptfusion : dv performance fix

Syncronization for Domain Validation workqueue and the initiation of the
alternate controller.  Its possible that dv could be terminated if the
workqueue on the 1st channel doesn complete in time before the 2nd channel
begins initialization.

Signed-off-by: Eric Moore <Eric.Moore@lsil.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>