hw/nvme: fix nvme hotplugging

Commit cd59f50ab017 caused a regression on nvme hotplugging for devices
with an implicit nvm subsystem.

The nvme-subsys device was incorrectly left with being marked as
non-hotpluggable. Fix this.

Cc: qemu-stable@nongnu.org
Reported-by: Stéphane Graber <stgraber@stgraber.org>
Tested-by: Stéphane Graber <stgraber@stgraber.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2950
Fixes: cd59f50ab017 ("hw/nvme: always initialize a subsystem")
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
(cherry picked from commit 0b1c23a582f7bc721a9b858c289a8d165152a6a0)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/nvme/subsys.c

@@ -226,7 +226,6 @@ static void nvme_subsys_class_init(ObjectClass *oc, void *data)
 
     dc->realize = nvme_subsys_realize;
     dc->desc = "Virtual NVMe subsystem";
-    dc->hotpluggable = false;
 
     device_class_set_props(dc, nvme_subsystem_props);
 }