ath11k: Update signal filled flag during sta_statistics drv op

Currently, though the peer rssi information is updated to station dump
from driver sta_statistics mac op, the info doesn't get updated
since the NL80211_STA_INFO_SIGNAL filled flag is not set in station
info. Hence update this flag while filling the rssi info.

Tested on: IPQ8074 WLAN.HK.2.1.0.1-01213-QCAHKSWPL_SILICONZ-1

Signed-off-by: Sriram R <srirrama@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210224090241.3098-1-srirrama@codeaurora.org