ar71xx: Fix UBIFS work on Mikrotik RB95x devices

If nand chip has no NAND_NO_SUBPAGE_WRITE flag on its options
ubifs can't use it mtd devices and the kernel crashes with error:
__nand_correct_data: uncorrectable ECC error

Signed-off-by: Sergey Sergeev <adron@yapic.net>

target/linux/ar71xx/files/arch/mips/ath79/mach-rb95x.c

@@ -165,6 +165,8 @@ static int rb95x_nand_scan_fixup(struct mtd_info *mtd)
 		chip->ecc.layout = &rb95x_nand_ecclayout;
 	}
 
+	chip->options = NAND_NO_SUBPAGE_WRITE;
+
 	return 0;
 }