wifi: rtw88: Rename RTW_RATE_SECTION_MAX to RTW_RATE_SECTION_NUM

It fits the meaning of the enum better.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/5a1c5a46-8ebb-43b0-9ab1-b78e2a22b3d2@gmail.com