drm/amdgpu: fix UBSAN array-index-out-of-bounds for ras_block_string[]

fix array index out of bounds issue for ras_block_string[] array.

Fixes: 30df05fb

 ("drm/amdgpu: Align ras block enum with firmware")
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>