acpi-update.py: there is no "Error" class

Evidently this code path was never hit, because we'd crash with NameError.
The exception message also seems bogus. So just replace the whole thing
with the standard exception for invalid input.

hwdb/acpi-update.py

@@ -31,7 +31,7 @@ class PNPTableParser(HTMLParser):
             elif self.state == State.AFTER_PNPID:
                 self.state = State.DATE
             else:
-                raise Error("Unexpected field")
+                raise ValueError
 
             self.data = ""
 
@@ -48,7 +48,7 @@ class PNPTableParser(HTMLParser):
             elif self.state == State.DATE:
                 self.state = State.NOWHERE
             else:
-                raise Error("Unexpected field")
+                raise ValueError
 
     def handle_data(self, data):
         self.data += data