drm/amdgpu: Fix build warning for TA debugfs interface

Remove the redundant codes to fix build warning
when CONFIG_DEBUG_FS is disabled.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Candice Li <candice.li@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>