rtlwifi: Extend tx_power_by_rate_offset size for newer IC

In older design, the TX power is grouped into rate section (smaller array
size), but new design groups them into rate (larger array size). Thus,
we extend the size for both cases, and add compile time assertion.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>