drm/amdgpu: avoid dump mca bank log muti times during ras ISR

because the ue valid mca count will only be cleared after gpu reset,
so only dump mca log on the first time to get mca bank after receive RAS interrupt.

Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>