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.
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
Link: https://lore.kernel.org/r/20230412093734.1126410-1-jiangfeng@kylinos.cnReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>