wifi: cfg80211: wext: Update spelling and grammar

Correct spelling in iw_handler.h.
As reported by codespell.

Also, while the "few shortcomings" line is being updated,
correct its grammar.

Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240903-wifi-spell-v2-1-bfcf7062face@kernel.org


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