mt76: mt7615: do not always reset the dfs state setting the channel

mac80211/hostapd runs mt7615_set_channel with the same channel
parameters sending multiple rdd commands overwriting the previous ones.
This behaviour is causing tpt issues on dfs channels.
Fix the issue checking new channel freq/width with the running one.

Fixes: 5dabdf71 ("mt76: mt7615: add multiple wiphy support to the dfs support code")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>