Drivers: hv: balloon: Use VMBUS_RING_SIZE() wrapper for dm_ring_size

Baihua reported an error when boot an ARM64 guest with PAGE_SIZE=64k and
BALLOON is enabled:

	hv_vmbus: registering driver hv_balloon
	hv_vmbus: probe failed for device 1eccfd72-4b41-45ef-b73a-4a6e44c12924 (-22)

The cause of this is that the ringbuffer size for hv_balloon is not
adjusted with VMBUS_RING_SIZE(), which makes the size not large enough
for ringbuffers on guest with PAGE_SIZE=64k. Therefore use
VMBUS_RING_SIZE() to calculate the ringbuffer size. Note that the old
size (20 * 1024) counts a 4k header in the total size, while
VMBUS_RING_SIZE() expects the parameter as the payload size, so use
16 * 1024.

Cc: <stable@vger.kernel.org> # 5.15.x
Reported-by: Baihua Lu <baihua.lu@microsoft.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20211101150026.736124-1-boqun.feng@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

drivers/hv/hv_balloon.c

@@ -480,7 +480,7 @@ module_param(pressure_report_delay, uint, (S_IRUGO | S_IWUSR));
 MODULE_PARM_DESC(pressure_report_delay, "Delay in secs in reporting pressure");
 static atomic_t trans_id = ATOMIC_INIT(0);
 
-static int dm_ring_size = 20 * 1024;
+static int dm_ring_size = VMBUS_RING_SIZE(16 * 1024);
 
 /*
  * Driver specific state.