regulator: pca9450: Use devm_register_sys_off_handler

In the Linux kernel, the following vulnerability has been resolved:

regulator: pca9450: Use devm_register_sys_off_handler

With module test, there is error dump: ------------[ cut here ]------------ notifier callback pca9450_i2c_restart_handler already registered WARNING: kernel/notifier.c:23 at notifier_chain_register+0x5c/0x88, CPU#0: kworker/u16:3/50 Call trace: notifier_chain_register+0x5c/0x88 (P) atomic_notifier_chain_register+0x30/0x58 register_restart_handler+0x1c/0x28 pca9450_i2c_probe+0x418/0x538 i2c_device_probe+0x220/0x3d0 really_probe+0x114/0x410 __driver_probe_device+0xa0/0x150 driver_probe_device+0x40/0x114 __device_attach_driver+0xd4/0x12c

So use devm_register_sys_off_handler to let kernel handle the resource free to avoid kernel dump.