drm/amdkfd: fix NULL dereference in get_queue_ids()

In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: fix NULL dereference in get_queue_ids() When usr_queue_id_array is NULL and num_queues is non-zero, get_queue_ids() returns NULL. The callers check only IS_ERR() on the return value; since IS_ERR(NULL) == false the check passes, and suspend_queues() calls q_array_invalidate() which immediately dereferences NULL while iterating num_queues times. Userspace can trigger this via kfd_ioctl_set_debug_trap() by supplying num_queues > 0 with a zero queue_array_ptr, causing a kernel panic. A NULL usr_queue_id_array with num_queues == 0 is a legitimate no-op (q_array_invalidate never executes, and resume_queues already guards all queue_ids dereferences behind a NULL check). Return ERR_PTR(-EINVAL) only when num_queues is non-zero and the pointer is absent; both callers already propagate IS_ERR() returns correctly to userspace. (cherry picked from commit f165a82cdf503884bb1797771c61b2fcc72113d4)