Cancelling an already cancelled command does not do anything, so check
the command context before cancelling it, continuing if had already been
cancelled so we do not log the same problem every second if a device
stops responding.
Signed-off-by: NKeith Busch <keith.busch@intel.com>
Signed-off-by: NMatthew Wilcox <matthew.r.wilcox@intel.com>