xenbus: check xen_domain in xenbus_probe_initcall

The same way we already do in xenbus_init.
Fixes the following warning:

[ 352.175563] Trying to free already-free IRQ 0
[ 352.177355] WARNING: CPU: 1 PID: 88 at kernel/irq/manage.c:1893 free_irq+0xbf/0x350
[...]
[ 352.213951] Call Trace:
[ 352.214390] <TASK>
[ 352.214717] ? __warn+0x81/0x170
[ 352.215436] ? free_irq+0xbf/0x350
[ 352.215906] ? report_bug+0x10b/0x200
[ 352.216408] ? prb_read_valid+0x17/0x20
[ 352.216926] ? handle_bug+0x44/0x80
[ 352.217409] ? exc_invalid_op+0x13/0x60
[ 352.217932] ? asm_exc_invalid_op+0x16/0x20
[ 352.218497] ? free_irq+0xbf/0x350
[ 352.218979] ? __pfx_xenbus_probe_thread+0x10/0x10
[ 352.219600] xenbus_probe+0x7a/0x80
[ 352.221030] xenbus_probe_thread+0x76/0xc0

Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain")
Signed-off-by: Stefano Stabellini <[e-mail]>
Tested-by: Petr Mladek <[e-mail]>
Reviewed-by: Oleksandr Tyshchenko <[e-mail]>

Link: https://lore.kernel.org/r/alpine.DEB.2.22.394.2307211609140.3118466@ubuntu-linux-20-04-desktop
Signed-off-by: Juergen Gross <[e-mail]>

drivers/xen/xenbus/xenbus_probe.c

···
 
 static int __init xenbus_probe_initcall(void)
 {
+	if (!xen_domain())
+		return -ENODEV;
+
 	/*
 	 * Probe XenBus here in the XS_PV case, and also XS_HVM unless we
 	 * need to wait for the platform PCI device to come up or