It turned out that we can run calibration without already received
frames with RSSI data. In such case just don't update AGC register
and don't print the warning.
Fixes: b305a6ab0247 ("mt7601u: use EWMA to calculate avg_rssi") Reported-by: Adam Borowski <kilobyte@angband.pl> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Acked-by: Jakub Kicinski <kubakici@wp.pl> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>