thermal: intel: x86_pkg_temp_thermal: Drop duplicate 'is' from comment

There is an unexpected word 'is' in a comments that need to be dropped

file: ./drivers/thermal/intel/x86_pkg_temp_thermal.c
line: 108

* tj-max is is interesting because threshold is set relative to this

changed to:

* tj-max is interesting because threshold is set relative to this

Signed-off-by: Jiang Jian <jiangjian@cdjrlc.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>