drm/amd/pp: Fix uninitialized variable

Initialize variable to 0 before performing logical OR operation.

Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Rajan Vaja <rajan.vaja@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>