drm/amdkfd: fix NULL dereference in get_queue_ids()

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.

Fixes: a70a93fa568b ("drm/amdkfd: add debug suspend and resume process queues operation")
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f165a82cdf503884bb1797771c61b2fcc72113d4)
Cc: stable@vger.kernel.org