drm/amdgpu: use irq-safe lock for kiq->ring_lock

This lock is used during register accessing in SRIOV guest.
The register accessing could happen both in irq enabled and
irq disabled cases. Always use irq-safe lock.

Signed-off-by: Pixel Ding <Pixel.Ding@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>