core/test: Use "" as the name of the device tree root node.
core/test: Use "" as the name of the device tree root node.

The device tree tests use "root" as the name of the root node. That
leads to weird discrepancies between the reported path and the
dt_find_by_path path.

The empty string is already used as the root name in dt_expand.

Signed-off-by: Daniel Axtens <cf1af486034ab0119a20f38a060e40da25f4cea3@axtens.net>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

mikey/skiboot,legoater/skiboot,open-power/skiboot,cyrilbur-ibm/skiboot,jk-ozlabs/skiboot,legoater/skiboot,stewart-ibm/skiboot,stewart-ibm/skiboot,qemu/skiboot,qemu/skiboot,shenki/skiboot,mikey/skiboot,stewart-ibm/skiboot,open-power/skiboot,csmart/skiboot,ddstreet/skiboot,shenki/skiboot,apopple/skiboot,legoater/skiboot,ddstreet/skiboot,qemu/skiboot,cyrilbur-ibm/skiboot,open-power/skiboot,cyrilbur-ibm/skiboot,open-power/skiboot,mikey/skiboot,qemu/skiboot,csmart/skiboot,ddstreet/skiboot,qemu/skiboot,open-power/skiboot,shenki/skiboot,apopple/skiboot,shenki/skiboot,shenki/skiboot,jk-ozlabs/skiboot,csmart/skiboot,apopple/skiboot,jk-ozlabs/skiboot,legoater/skiboot,legoater/skiboot