drm/amdgpu: Fix memory leak in amdgpu_ctx_mgr_entity_fini

patch dd649566 ("drm/amdgpu: Remove duplicated "context still
alive" check") removed ctx put, which will cause amdgpu_ctx_fini()
cannot be called and then cause some finished fence that added by
amdgpu_ctx_add_fence() cannot be released and cause memleak.

Fixes: dd649566 ("drm/amdgpu: Remove duplicated "context still alive" check")
Signed-off-by: Lin.Cao <lincao12@amd.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>