cfg80211: remove switch from __regulatory_hint()

We have complete control over REGDOM_SET_BY_* enum passed
down to __regulatory_hint() as such there is no need to
account for unexpected REGDOM_SET_BY_*'s, lets just remove
the switch statement as this code does not change and
won't change even when we add 802.11d support.

This patch has no functional changes.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>