platform/x86/amd: pmc: Fix memory leak in amd_pmc_stb_debugfs_open_v2()

In the Linux kernel, the following vulnerability has been resolved: platform/x86/amd: pmc: Fix memory leak in amd_pmc_stb_debugfs_open_v2() Function amd_pmc_stb_debugfs_open_v2() may be called when the STB debug mechanism enabled. When amd_pmc_send_cmd() fails, the 'buf' needs to be released.