MFC r264354 but change the lock arg and implementation to fit the current state
of CAM in stable/9

Fix insta-panic on assert of unlocked periph mtx in ciss(4) when
logical volume state changes.

I'm still setting the mergeinfo as done here as the intent of the MFC, if not
the EXACT code is being implemented.

Reviewed by:	mav@
Sponsored by:	Yahoo! Inc