rtlwifi: rtl8192cu: Fix NULL dereference BUG when using new_id

commit 957f4aca5fa0db69635271bc4621cc0b65b2d590 upstream.

When the new_id entry in /sysfs is used for a foreign USB device, rtlwifi
BUGS with a NULL pointer dereference because the per-driver configuration
data is not available. The probe function has been restructured as
suggested by Ben Hutchings <bhutchings@solarflare.com>.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>