kernel: rtl8367b: fix external interface modes

kernel: rtl8367b: fix external interface modes

The interface mode number of RGMII_33V is 7 on RTL8367, but it's 9 on
RTL8367B.

the external interface modes for RTL8367 are follows:

- 0, Disabled
- 1, RGMII
- 2, MII_MAC
- 3, MII_PHY
- 4, TMII_MAC
- 5, TMII_PHY
- 6, GMII
- 7, RGMII_33V

the external interface modes for RTL8367B are follows:

- 0, Disabled
- 1, RGMII
- 2, MII_MAC
- 3, MII_PHY
- 4, TMII_MAC
- 5, TMII_PHY
- 6, GMII
- 7, RMII_MAC
- 8, RMII_PHY
- 9, RGMII_33V

But the driver in U-Boot of RT-N56U GPL tar blocks using RGMII_33V (9)
mode and it seems to be unsupported on RTL8367B, so drop it from
switch-case in rtl8367b_extif_set_mode.

ref (RTL8367):

- TL-WR2453ND v1

ref (RTL8367B):

- ASUS RT-N56U
- TP-Link Archer C2 v1

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>