afs: Fix some tracing details

Fix a couple of tracelines to indicate the usage count after the atomic op,
not the usage count before it to be consistent with other afs and rxrpc
trace lines.

Change the wording of the afs_call_trace_work trace ID label from "WORK" to
"QUEUE" to reflect the fact that it's queueing work, not doing work.

Fixes: 341f741f ("afs: Refcount the afs_call struct")
Signed-off-by: David Howells <dhowells@redhat.com>