hwmon: (ibmpex) fix use-after-free in high/low store

In the Linux kernel, the following vulnerability has been resolved: hwmon: (ibmpex) fix use-after-free in high/low store The ibmpex_high_low_store() function retrieves driver data using dev_get_drvdata() and uses it without validation. This creates a race condition where the sysfs callback can be invoked after the data structure is freed, leading to use-after-free. Fix by adding a NULL check after dev_get_drvdata(), and reordering operations in the deletion path to prevent TOCTOU.