rtw89: remove duplicate definition of hardware port number

RTW89_MAX_HW_PORT_NUM and RTW89_PORT_NUM refer to the same thing, so remove
the one of them.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211227083134.35248-1-pkshih@realtek.com