drm/amdkfd: fix a potential NULL pointer dereference (v2)

alloc_workqueue is not checked for errors and as a result,
a potential NULL dereference could occur.

v2 (Felix Kuehling):
* Fix compile error (kfifo_free instead of fifo_free)
* Return proper error code
Signed-off-by: Allen Pais <allen.pais@oracle.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -62,6 +62,11 @@ int kfd_interrupt_init(struct kfd_dev *kfd)
 	}
 
 	kfd->ih_wq = alloc_workqueue("KFD IH", WQ_HIGHPRI, 1);
+	if (unlikely(!kfd->ih_wq)) {
+		kfifo_free(&kfd->ih_fifo);
+		dev_err(kfd_chardev(), "Failed to allocate KFD IH workqueue\n");
+		return -ENOMEM;
+	}
 	spin_lock_init(&kfd->interrupt_lock);
 
 	INIT_WORK(&kfd->interrupt_work, interrupt_wq);