cpufreq: light-mpw-cpufreq: fix cpu_pll1 already disabled warning

[pdp7]

• Fix warning in light_set_target() during boot that cpu_pll1_foutpostdiv was already disabled. Only call clk_disable_unprepare() for LIGHT_CPU_PLL0_FOUTPOSTDIV if clk_set_parent() returns non-zero value.

  • Boot log with warning: linux-image-6.8.0-rc1-g4e4b0c0fcf8a_6.8.0-rc1-g4e4b0c0fcf8a-20_riscv64.txt
  • Boot log after fixing: linux-image-6.8.0-rc1-g1229138d8c71_6.8.0-rc1-g1229138d8c71-38_riscv64.deb.log

• minor fix for -Wunused-variable warning in panic_cpufreq_notifier_call()

[RevySR]

merged th1520-v6.8-wip