vendor_upsd: fix schema not getting created

The previous call to object_names won't provide the type and permission of the object/parameter, which is required for adding to object to USP.

• Parses the blobmsg direclty without converting it to json first.
• Use get_names_safe to get type and permissions of object

Signed-off-by: Daniel Danzberger daniel@dd-wrt.com

@vdutta