dmaengine: ioatdma: Fix missing kmem_cache_destroy()

Fix missing kmem_cache_destroy() for ioat_sed_cache in
ioat_exit_module().

Noticed via:

```
modprobe ioatdma
rmmod ioatdma
modprobe ioatdma
debugfs: Directory 'ioat_sed_ent' with parent 'slab' already present!
```

Fixes: c0f28ce66ecf ("dmaengine: ioatdma: move all the init routines")
Signed-off-by: Nikita Shubin <[e-mail]>
Acked-by: Dave Jiang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/ioat/init.c

···
 static void __exit ioat_exit_module(void)
 {
 	pci_unregister_driver(&ioat_pci_driver);
+	kmem_cache_destroy(ioat_sed_cache);
 	kmem_cache_destroy(ioat_cache);
 }
 module_exit(ioat_exit_module);