ath11k: fix missed bw conversion in tx completion

TX rate stats for the retried packets for a station comes through
tx completion events. Assigning hw reported bandwidth information
directly to station's txrate bandwidth will cause below warning.
Fix this warning by converting the hw reported bandwidth to
mac80211 base bandwidth.

[ 134.758190] PC is at cfg80211_calculate_bitrate+0x1bc/0x214 [cfg80211]
[ 134.765730] LR is at cfg80211_calculate_bitrate+0x1bc/0x214 [cfg80211]
[ 134.875014] [<ffffffbffca8d708>] cfg80211_calculate_bitrate+0x1bc/0x214 [cfg80211]
[ 134.877192] [<ffffffbffcaa9704>] nl80211_put_sta_rate+0x54/0xf24 [cfg80211]
[ 134.884829] [<ffffffbffcaa9d48>] nl80211_put_sta_rate+0x698/0xf24 [cfg80211]
[ 134.891687] [<ffffffbffcaaa490>] nl80211_put_sta_rate+0xde0/0xf24 [cfg80211]
[ 134.898975] [<ffffffc0004de748>] genl_lock_dumpit+0x30/0x4c
[ 134.905998] [<ffffffc0004dc264>] netlink_dump+0xf4/0x248
[ 134.911291] [<ffffffc0004dc910>] __netlink_dump_start+0xe0/0x174
[ 134.916850] [<ffffffc0004df114>] genl_family_rcv_msg+0x130/0x2c0

Signed-off-by: Tamizh chelvam <tamizhr@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>