wifi: iwlwifi: mld: fix chandef start calculation

wifi: iwlwifi: mld: fix chandef start calculation

A link pair in which both links are in 5 GHz can be used for EMLSR only
if they are separated enough.

To check this condition we calculate the start and the end of the
chandefs of both links in the pair and do some checks.

But the calculation of the start/end of the chandef is currently done
by subtracting/adding half the bandwidth from/to the control channel's
center frequency, when it should really be subtracted/added from/to the
center frequency of the entire chandef.

Fix the wrong calculation.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260111193638.2138fdb99bd5.I4d2e5957b22482a57b1d6ca444e90fcf73bf2cab@changeid