rt2x00: Fix SLAB corruption during rmmod

rt2x00: Fix SLAB corruption during rmmod

At rmmod stage, the code path is the following one :

rt2x00lib_remove_dev
  ->  rt2x00lib_uninitialize()
        -> rt2x00rfkill_unregister()
             -> rfkill_unregister()
        -> rt2x00rfkill_free()
             -> rfkill_free()

The problem is that rfkill_free should not be called after rfkill_register
otherwise put_device(&rfkill->dev) will be called 2 times. This patch
fixes this by only calling rt2x00rfkill_free() when rt2x00rfkill_register()
hasn't been called or has failed.

This patch is for 2.6.29 only. The code in question has completely disappeared
in 2.6.30 and does not contain this bug.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Tested-by: Arnaud Patard <apatard@mandriva.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>