wifi: nl80211: return error message for malformed chandef

Add an error message to the missing frequency case to have all
-EINVAL in nl80211_parse_chandef() return a better error.

Signed-off-by: Jaewan Kim <jaewan@google.com>
Link: https://lore.kernel.org/r/20230130074514.1560021-1-jaewan@google.com
[rewrite commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>