powercap: dtpm: Fix kernel-doc for dtpm_create_hierarchy() function

The existing comment block above the dtpm_create_hierarchy function
does not conform to the kernel-doc standard. This patch fixes the
documentation to match the expected kernel-doc format, which includes
a structured documentation header with param and return value.

Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>