ath10k: fix pointless update of peer stats list

We periodically receive f/w stats event for updating
the rx duration and there is no reason to keep on appending
the f/w stats peer list, as this gets completely cleaned up when
the user polls for f/w stats {pdev, vdev, peer stats}. Only don't
print the warning message in the case PEER_STATS service is enabled

Fixes: 856e7c30 ("ath10k: add debugfs support for Per STA total rx duration")
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>