wifi: iwlwifi: use 0xff instead of 0xffffffff for invalid

The firmware is now able to understand 0xff and that is more widely
used.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250212073923.c6719e6dc0a6.Ifd149101fa886730602dbbb02f980be8e554fe84@changeid


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