rtlwifi: Remove extra workqueue for enter/leave power state

When the rtlwifi family of drivers was converted to use a workqueue when
entering or leaving power save mode (commits a269913c, a5ffbe0a,
41affd52, b9116b9a, and 6539306b), the code began scheduling work from
the callback routine of a different workqueue with a resulting increase in
overhead.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>