drm/amd/pp: remove redundant pointer internal_buf

The pointer internal_buf is assigned a value but the pointer is never
read, hence it is redundant and can be removed.

Cleans up clang warning:
drivers/gpu/drm/amd/amdgpu/../powerplay/smumgr/smu7_smumgr.c:630:2:
warning: Value stored to 'internal_buf' is never read

Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>