cfg80211: get rid of name indirection trick for ieee80211_get_channel()

The comment on the name indirection suggested an issue but turned out
to be untrue. Digging in older kernel version showed issue with ipw2x00
but that is no longer true so get rid on the name indirection.

Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>