Fix gradient is ready with z2

[sfc-gh-truwase]

Correctly handle ds_grad_is_ready in ZeRO2

[stas00]

Interesting, thanks for finding this, Tunji, so then we don't need the condition at:

DeepSpeed/deepspeed/runtime/zero/stage_1_and_2.py

Line 1084 in 6b9cab1

if getattr(param, "ds_grad_is_ready", True):

as your added check will prevent it from ever being False at l1084