thermal/x86_pkg_temp: Replace open coded cpu search

find_next_sibling() iterates over the online cpus and searches for a cpu
with the same package id as the current cpu. This is a pointless exercise
as topology_core_cpumask() allows a simple cpumask search for an online cpu
on the same package.

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>