Function radeon_ring_lock() returns an errno on failure, and its return
value should be validated. However, in functions r420_cp_errata_init()
and r420_cp_errata_fini(), its return value is not checked. This patch
adds the checks.
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NPan Bian <bianpan2016@163.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>