cfg80211: remove superfluous !last_request check in reg_device_remove()

Commit 0ad8acaf "cfg80211: fix NULL pointer deference in
reg_device_remove()" added a check that last_request is non-NULL,
rendering the 2nd check superfluous.  While there, rearrange the code a
bit so it's a little more straight forward.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>