mediatek: cudy nand: fix wrong nmbm configuration

mediatek: cudy nand: fix wrong nmbm configuration

Nmbm is mistakenly enabled on ubootmod builds of nand Cudy routers:
------------------------------------------------------------------------
[    0.923433] spi-nand spi0.0: calibration result: 0x3
[    0.928485] spi-nand spi0.0: ESMT SPI NAND was found.
[    0.933560] spi-nand spi0.0: 128 MiB, block size: 128 KiB, page size:
2048, OOB size: 64
[    1.828275] Signature not found
-------------------------------------------------------------------------

This commit disables nmbm for such builds.

Fixes: eb6dd61 ("mediatek: add cudy wr3000h-v1 ubootmod")
Fixes: cfc17e8 ("mediatek: add cudy wr3000e-v1 ubootmod")
Fixes: 6b3b7c7 ("mediatek: add cudy wr3000p-v1 ubootmod")
Fixes: b7b4938 ("mediatek: add cudy wr3000s-v1 ubootmod")
Fixes: 15df98f ("mediatek: add ubootmod layout for Cudy WBR3000UAX v1")
Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22832
Signed-off-by: Robert Marko <robimarko@gmail.com>