rtw89: fill regd field of limit/limit_ru tables by enum

This modification just replaces the number filled in the regd field
with the corresponding enum. No assignment of a value in a table is
changed. Doing this first is because the follow-up patches may adjust
the order of enum declarations.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211101093106.28848-2-pkshih@realtek.com