ath10k: fill HT/VHT MCS rateset only for configured chainmask

HT/VHT MCS rateset should be filled only for configured chainmask
rather that max supported chainmask. Fix that by checking configured
chainmask while filling HT/VHT MCS rate map.

Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>