drivers/base/memory: Fix an unlikely reference counting issue in __add_memory_block()

__add_memory_block() calls both put_device() and device_unregister() when
storing the memory block into the xarray. This is incorrect because xarray
doesn't take an additional reference and device_unregister() already calls
put_device().

Triggering the issue looks really unlikely and its only effect should be to
log a spurious warning about a ref counted issue.

Fixes: 4fb6eabf ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/d44c63d78affe844f020dc02ad6af29abc448fc4.1650611702.git.christophe.jaillet@wanadoo.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/memory.c

@@ -636,10 +636,9 @@ static int __add_memory_block(struct memory_block *memory)
 	}
 	ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
 			      GFP_KERNEL));
-	if (ret) {
-		put_device(&memory->dev);
+	if (ret)
 		device_unregister(&memory->dev);
-	}
+
 	return ret;
 }