iio: adc: mt6359: fix unchecked return value in mt6358_read_imp

In the Linux kernel, the following vulnerability has been resolved: iio: adc: mt6359: fix unchecked return value in mt6358_read_imp In mt6358_read_imp(), the variable val_v is passed to regmap_read() but the return value is not checked. If the read fails, val_v remains uninitialized and its random stack content is subsequently reported as a measurement result. Initialize val_v to zero to ensure a predictable value is reported in case of bus failure and to prevent potential stack data leakage. This also satisfies static analyzers that might otherwise flag the variable as used uninitialized.