wifi: mac80211: correct EHT EIRP TPE parsing

wifi: mac80211: correct EHT EIRP TPE parsing

For the EHT EIRP transmit power envelope, the 320 MHz is in
the last octet, but if we've copied 4 octets (count == 3),
the next one is at index 4 not 5 (count + 2). Fix this, and
just hardcode the offset since count is always 3 here.

Fixes: 39dc8b8ea387 ("wifi: mac80211: pass parsed TPE data to drivers")
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240612100533.f96c1e0fb758.I2f301c4341abb44dafd29128e7e32c66dc0e296d@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>