CVE-2026-98931: mtd: spinand: fix NULL pointer dereference with no ECC engine

In the Linux kernel, the following vulnerability has been resolved:

mtd: spinand: fix NULL pointer dereference with no ECC engine

When "nand-no-ecc-engine" is set in DT, nanddevgeteccengine() takes the NANDECCENGINETYPENONE path and returns success while leaving nand->ecc.engine NULL. The SPI-NAND code nevertheless dereferences it unconditionally to test for a pipelined engine, so probing such a device oopses immediately.

Rather than open-coding the test three times, add a nandeccispipelined() helper to the NAND core that folds the NULL check into the integration comparison, and use it everywhere. Future callers then cannot reintroduce the problem.