ath9k: Fix noisefloor calibration

ath9k: Fix noisefloor calibration

The commits,

"ath9k: Fix regression in channelwidth switch at the same channel"
"ath9k: Fix invalid noisefloor reading due to channel update"

attempted to fix noisefloor calibration when a channel switch
happens due to HT20/HT40 bandwidth change. This is causing invalid
readings resulting in messages like:

"ath: phy16: NF[0] (-45) > MAX (-95), correcting to MAX".

This results in an incorrect noise being used initially for reporting
the signal level of received packets, until NF calibration is done
and the history buffer is updated via the ANI timer, which happens
much later.

When a bandwidth change happens, it is appropriate to reset
the internal history data for the channel. Do this correctly in the
reset() routine by checking the "chanmode" variable.

Cc: stable@vger.kernel.org
Cc: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>