hw_inventory: fix json parsing

Add support for both lshw -json return formats.
The json structure may follow one of the following.

output:list flag enabled:
[{content}]

output:list flag disabled:
{content}

The output:list flag was defined in the commit 2b1c730 of
https://ezix.org/src/pkg/lshw

src/utils/hw_inventory.py

@@ -293,10 +293,10 @@ def legacy_list_hardware_inventory(inventory):
 
 def get_hardware_inventory():
     proc = subprocess.run(['lshw', '-json'], stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
-    j = json.loads(proc.stdout)
+    root = json.loads(proc.stdout)
 
-    if type(j) is list:
-        root = j[0]
+    if type(root) is list:
+        root = root[0]
     if type(root) is not dict:
         raise OgError('Invalid lshw json output')