mac80211: correct probe wait time

My first patch submission used 200ms, which I then somehow
managed to revert back to the earlier 50ms I had used for
some tests in the second patch submission -- but that was
wrong, I should have used 200ms here. Correct that.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>