r8169: add missing MODULE_FIRMWARE.

Leftover from 6e1d0b89 ("r8169:add
support for RTL8168H and RTL8107E").

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Chun-Hao Lin <hau@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>