ath9k: fix misc debugfs when not using chan context

When channel-context is not enabled, all vifs belong to
the first context, but it is not configured as 'assigned'.

Fix misc debugfs file to print out info for non-assigned
contexts, and also print whether ctx is assigned or not.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>