wireless: reg: restore previous behaviour of chan->max_power calculations

commit eccc068e
Author: Hong Wu <Hong.Wu@dspg.com>
Date:   Wed Jan 11 20:33:39 2012 +0200

    wireless: Save original maximum regulatory transmission power for the calucation of the local maximum transmit pow

changed the way we calculate chan->max_power as min(chan->max_power,
chan->max_reg_power). That broke rt2x00 (and perhaps some other
drivers) that do not set chan->max_power. It is not so easy to fix this
problem correctly in rt2x00.

According to commit eccc068e

 changelog, change claim only to save
maximum regulatory power - changing setting of chan->max_power was side
effect. This patch restore previous calculations of chan->max_power and
do not touch chan->max_reg_power.

Cc: stable@vger.kernel.org # 3.4+
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>