drm/amd/amdkfd: Drop unnecessary NULL check after container_of

The first parameter passed to container_of() is the pointer to the work
structure passed to the worker and never NULL. The NULL check on the
result of container_of() is therefore unnecessary and misleading.
Remove it.

This change was made automatically with the following Coccinelle script.

@@
type t;
identifier v;
statement s;
@@

<+...
(
  t v = container_of(...);
|
  v = container_of(...);
)
  ...
  when != v
- if (\( !v \| v == NULL \) ) s
...+>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_process.c

@@ -110,8 +110,6 @@ static void kfd_sdma_activity_worker(struct work_struct *work)
 
 	workarea = container_of(work, struct kfd_sdma_activity_handler_workarea,
 				sdma_activity_work);
-	if (!workarea)
-		return;
 
 	pdd = workarea->pdd;
 	if (!pdd)