riscv: dts: sophgo: disable write-protection for milkv duo

Milkv Duo does not have a write-protect pin, so disable write protect
to prevent SDcards misdetected as read-only.

Fixes: 89a7056e

 ("riscv: dts: sophgo: add sdcard support for milkv duo")
Signed-off-by: Haylen Chu <heylenay@outlook.com>
Link: https://lore.kernel.org/r/SEYPR01MB4221943C7B101DD2318DA0D3D7CE2@SEYPR01MB4221.apcprd01.prod.exchangelabs.com
Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>