nl80211: Fix offloaded ACS regression for the 60 GHz band

nl80211: Fix offloaded ACS regression for the 60 GHz band

Addition of chan_2ghz_or_5ghz_to_freq() broke 60 GHz ACS, because it
assumes reported ACS channel is on either 2.4 or 5 GHz band. Fix this
by converting chan_2ghz_or_5ghz_to_freq() to a more generic
chan_to_freq(). The new function uses hw_mode to support 60 GHz.

Fixes: 41cac481a889 ("ACS: Use frequency params in ACS (offload) completed event interface")
Signed-off-by: Noam Shaked <nshaked@codeaurora.org>