mtd: nand: ecc-mxic: Fix use of uninitialized variable ret

In the Linux kernel, the following vulnerability has been resolved: mtd: nand: ecc-mxic: Fix use of uninitialized variable ret If ctx->steps is zero, the loop processing ECC steps is skipped, and the variable ret remains uninitialized. It is later checked and returned, which leads to undefined behavior and may cause unpredictable results in user space or kernel crashes. This scenario can be triggered in edge cases such as misconfigured geometry, ECC engine misuse, or if ctx->steps is not validated after initialization. Initialize ret to zero before the loop to ensure correct and safe behavior regardless of the ctx->steps value. Found by Linux Verification Center (linuxtesting.org) with SVACE.