Depending on which method the driver implements, userspace could
call this (indirectly, by getting station info) before the driver
knows about the station, possibly causing it to misbehave.

Therefore, add a check for sta->uploaded which indicates that the
driver knows about the station.
Signed-off-by: Maxim Altshul <maxim.altshul@ti.com>
[reword commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>