Documentation: powerclamp: Escape wildcard in cpumask description

kernel test robot reported htmldocs warning:

Documentation/admin-guide/thermal/intel_powerclamp.rst:328: WARNING: Inline emphasis start-string without end-string.

The mistaken asterisk in /proc/irq/*/smp_affinity is rendered as hyperlink
as the result.

Escape the asterisk to fix above warning.

Link: https://lore.kernel.org/linux-doc/202302122247.N4S791c4-lkp@intel.com/


Fixes: ebf51971 ("thermal: intel: powerclamp: Add two module parameters")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>