platform/x86/amd/pmc: Fix LPS0 and debugfs leaks when STB init fails

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

platform/x86/amd/pmc: Fix LPS0 and debugfs leaks when STB init fails

amd_pmc_probe() registers the LPS0 s2idle handler with
acpi_register_lps0_dev() and creates the driver's debugfs directory before
calling amd_stb_s2d_init(), which is the last step in probe that can fail.

When amd_stb_s2d_init() fails (for example the S2D telemetry region cannot
be ioremapped on a long-running system, or the SMU rejects the S2D setup)
the error path only calls pci_dev_put() and returns. This leaves
amd_pmc_s2idle_dev_ops on the global lps0_s2idle_devops_head list and leaks
the debugfs directory, while the devm-managed resources backing the handler
are torn down.

Reloading the module then walks the corrupted list in
acpi_register_lps0_dev() and hits:

list_add corruption. next->prev should be prev, but was NULL.
kernel BUG at lib/list_debug.c:29!
acpi_register_lps0_dev+0x44/0x80
amd_pmc_probe+0x224/0x380 [amd_pmc]
platform_probe+0x67/0x90

Even without a reload, the stale registration means the next s2idle
transition calls into torn-down driver state.

Unwind the debugfs directory and the LPS0 registration on the
amd_stb_s2d_init() error path. acpi_unregister_lps0_dev() is safe to call
unconditionally here: it is guarded on the same conditions as
acpi_register_lps0_dev(), which is exactly what amd_pmc_remove() already
relies on.