thermal/x86_pkg_temp: Cleanup code some more

Coding style fixups and replacement of overly complex constructs and random
error codes instead of returning the real ones. This mess makes the eyes bleeding.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>