nl80211: Fix possible Spectre-v1 for NL80211_TXRATE_HT

[ Upstream commit 30fe6d50eb088783c8729c7d930f65296b2b3fa7 ]

Use array_index_nospec() to sanitize ridx with respect to speculation.

Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>