rtlwifi: rtl8192de: Style clean-ups

[ Upstream commit 69831173 ]

Clean up some style issues:
- Use ARRAY_SIZE() even though it's a u8 array.
- Remove redundant CHANNEL_MAX_NUMBER_2G define.
Additionally fix some dead code WARNs.

Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://lore.kernel.org/lkml/57d0d1b6064342309f680f692192556c@realtek.com/


Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211119192233.1021063-1-keescook@chromium.org


Stable-dep-of: de4d4be4 ("wifi: rtlwifi: rtl8192de: Fix 5 GHz TX power")
Signed-off-by: Sasha Levin <sashal@kernel.org>