drm/amd/amdgpu: fix missing lock for cper.ring->rptr/wptr access

drm/amd/amdgpu: fix missing lock for cper.ring->rptr/wptr access

commit 8e0d1edb5c16732b695eaf4bd7096b1569817cf0 upstream.

Add lock protection for 'ring->wptr'/'ring->rptr' to ensure the correct execution.

Fixes: 8652920d2c00 ("drm/amdgpu: add mutex lock for cper ring")
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>