gpio: prevent potential speculation leaks in gpio_device_get_desc()

In the Linux kernel, the following vulnerability has been resolved: gpio: prevent potential speculation leaks in gpio_device_get_desc() Userspace may trigger a speculative read of an address outside the gpio descriptor array. Users can do that by calling gpio_ioctl() with an offset out of range. Offset is copied from user and then used as an array index to get the gpio descriptor without sanitization in gpio_device_get_desc(). This change ensures that the offset is sanitized by using array_index_nospec() to mitigate any possibility of speculative information leaks. This bug was discovered and resolved using Coverity Static Analysis Security Testing (SAST) by Synopsys, Inc.