isci: Fix RNC AWAIT_SUSPENSION->INVALIDATING transition.

The RNC state machine would incorrectly transition from
SCI_RNC_AWAIT_SUSPENSION directly to SCI_RNC_INVALIDATING when a destruct
request was made.  This would skip the increment of the suspension count
and the abort of pending TCs (although the invalidating state would at
least cleanup outstanding TCs).

Instead, the RNC will transition to SCI_RNC_SUSPENDED and then start the
destruction process.

Signed-off-by: Jeff Skirvin <jeffrey.d.skirvin@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>