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.