wifi: iwlwifi: api: fix center_freq label in PHY diagram

Somehow I managed to put the EHT line in the wrong place and
also didn't indent the center_freq label correctly. Fix it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20231017115047.08ac3cf524c0.I538f424e1ab30f73b0af8381224f377893e15526@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>