ath10k: fix invalid survey reporting for QCA99X0

There are three WMI_CHAN_INFO events reported per channel
in QCA99X0 firmware. First one is a notification at the begining
of the channel dwell time with cmd_flag as CHAN_INFO_START(cmd_flag = 0),
second one is a notification at the end of the dwell time with cmd_flag
CHAN_INFO_PRE_COMPLETE (cmd_flag = 2) and the third is the indication
with CHAN_INFO_COMPLETE (cmd_flag = 1) which is the last indication for
the channel. Since there is a new state before the completion, the handler
is to fixed so that the counts are deducted from the ones reported with
CHAN_INFO_START rather than the ones reported with CHAN_INFO_PRE_COMPLETE.
Without this fix there will be lots of 0 msecs reported as active
and busy time.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>