LinuxKPI / iwlwifi: fix spelling of constants

Fix the spelling of IEEE80211_HE_PHY_CAP9_NOMINAL_PKT_PADDING_*
(was "NOMIMAL"). The original version came from iwlwifi
in iwlwifi-next. Other drivers (from wireless-testing) already
use the correct spelling and need this change in LinuxKPI.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days