xenbus: fix error exit in xenbus_init()

In case an error occurs in xenbus_init(), xen_store_domain_type should
be set to XS_UNKNOWN.

Fix one instance where this action is missing.

Fixes: 5b335394 ("xen: add support for initializing xenstore later as HVM domain")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/202304200845.w7m4kXZr-lkp@intel.com/


Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Link: https://lore.kernel.org/r/20230822091138.4765-1-jgross@suse.com


Signed-off-by: Juergen Gross <jgross@suse.com>