dm raid: fix restoring of failed devices regression

'lvchange --refresh RaidLV' causes a mapped device suspend/resume cycle
aiming at device restore and resync after transient device failures.  This
failed because flag RT_FLAG_RS_RESUMED was always cleared in the suspend path,
thus the device restore wasn't performed in the resume path.

Solve by removing RT_FLAG_RS_RESUMED from the suspend path and resume
unconditionally.  Also, remove superfluous comment from raid_resume().

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>