drm/amdgpu: check memory allocation failure

Check memory allocation failure and return -ENOMEM in such a case.

'num_post_dep_syncobjs' still has to be set to 0 before the test in order
to have it initialized if 'amdgpu_cs_parser_fini()' is called to free
resources.

The calling graph would be, in such a case!
   failure in amdgpu_cs_process_syncobj_out_dep()
      ---> error code returned by amdgpu_cs_dependencies()
         --> amdgpu_cs_parser_fini() is called
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -1079,6 +1079,9 @@ static int amdgpu_cs_process_syncobj_out_dep(struct amdgpu_cs_parser *p,
 					     GFP_KERNEL);
 	p->num_post_dep_syncobjs = 0;
 
+	if (!p->post_dep_syncobjs)
+		return -ENOMEM;
+
 	for (i = 0; i < num_deps; ++i) {
 		p->post_dep_syncobjs[i] = drm_syncobj_find(p->filp, deps[i].handle);
 		if (!p->post_dep_syncobjs[i])