platform/x86: amd-pmc: Fix CONFIG_DEBUG_FS check

lkp reported that CONFIG_DEBUG_FS was not defined because of wrong usage
if macro, correcting it now.

Fixes: 156ec473

 ("platform/x86: amd-pmc: Add AMD platform support for S2Idle")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20201230081028.2615217-1-Shyam-sundar.S-k@amd.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>