drm/nouveau/devinit/nva3-: fix returnvar.cocci warning

Fix the following coccicheck warning:
drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gt215.c:71:5-12:
Unneeded variable: "disable". Return "0ULL" on line 85.

Signed-off-by: Guo Zhengkui <[e-mail]>
Reviewed-by: Lyude Paul <[e-mail]>
Signed-off-by: Lyude Paul <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gt215.c

···
 	struct nvkm_device *device = init->subdev.device;
 	u32 r001540 = nvkm_rd32(device, 0x001540);
 	u32 r00154c = nvkm_rd32(device, 0x00154c);
-	u64 disable = 0ULL;
 
 	if (!(r001540 & 0x40000000)) {
 		nvkm_subdev_disable(device, NVKM_ENGINE_MSPDEC, 0);
···
 	if (!(r00154c & 0x00000200))
 		nvkm_subdev_disable(device, NVKM_ENGINE_CE, 0);
 
-	return disable;
+	return 0ULL;
 }
 
 static u32