wifi: mac80211: align ieee80211_mle_get_bss_param_ch_cnt()

Align the prototype of ieee80211_mle_get_bss_param_ch_cnt()
to also take a u8 * like the other functions, and make it
return -1 when the field isn't found, so that mac80211 can
check that instead of explicitly open-coding the check.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240216135047.583309181bc3.Ia61cb0b4fc034d5ac8fcfaf6f6fb2e115fadafe7@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>