drm/amdgpu: fix ras ctrl debugfs node leak

Use debugfs_remove_recursive to remove the whole debugfs
directory instead of removing the node one by one.

Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>