The cam_sim structure was being deallocated unconditionally by device

The cam_sim structure was being deallocated unconditionally by device
driver detach routines.  The problem with this is that part of the CAM
bus structure may still be active (for example, with pending timeout()'s),
and even though the bus, target, and device is freed, since the sim IS
freed any accesses through the sim will hit 0xdeadc0de.  This case most often
occurs with USB UMASS devices.