wimax: depend on rfkill properly

My mistake, I should have added that when cleaning up
rfkill and changing wimax.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>