Now that no one is relying on the return value being a pointer to
somewhere inside of the passed-in argument, we can simplify the
callers to simply return success or failure.  Also wrap some long
lines and add some const-correctness.

* src/util/sysinfo.c (virSysinfoParseBIOS, virSysinfoParseSystem)
(virSysinfoParseProcessor, virSysinfoParseMemory): Change return.
(virSysinfoRead): Adjust caller.