fix qcom_cpu_kpssv2 compile on ASUS_AC1300

Complete afdb42987ca8 by changing the return type from boolean_t to bool
for the definition for qcom_cpu_kpssv2_regulator_start.

PR: 271932
Fixes: afdb42987ca82869eeaecf6dc25c2b6fb7b8370e
Pull Request: https://github.com/freebsd/freebsd-src/pull/776