thermal/debugfs: replace kzalloc() with kcalloc() in thermal_debug_tz_add()

thermal/debugfs: replace kzalloc() with kcalloc() in thermal_debug_tz_add()

Work is under way to get rid of all multiplications from allocation
functions to prevent integer overflows [1].

Here the multiplication is obviously safe, but using kcalloc() is more
appropriate and improves readability.

This change has no effect on runtime behavior.

Link: https://github.com/KSPP/linux/issues/162
Signed-off-by: Ethan Carter Edwards <ethan@ethancedwards.com>
Link: https://patch.msgid.link/20250222-thermal_kcalloc-v1-1-9f7a747fbed7@ethancedwards.com
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>