drm/amdgpu: change to save bad pages in UMC error interrupt callback

Instead of saving bad pages in amdgpu_ras_reset_gpu, it will reduce
the unnecessary calling of amdgpu_ras_save_bad_pages.

Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Reviewed-by: Hawking Zhang <hawking.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>