drm/hyperv: Don't overwrite dirt_needed value set by host

Existing code is causing a race condition where dirt_needed value is
already set by the host and gets overwritten with default value. Remove
this default setting of dirt_needed, to avoid overwriting the value
received in the channel callback set by vmbus_open. Removing this
setting also means the default value for dirt_needed is changed to false
as it's allocated by kzalloc which is similar to legacy hyperv_fb driver.

Signed-off-by: Saurabh Sengar <[e-mail]>
Reviewed-by: Dexuan Cui <[e-mail]>
Reviewed-by: Michael Kelley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Wei Liu <[e-mail]>

drivers/gpu/drm/hyperv/hyperv_drm_drv.c

···
 	if (ret)
 		drm_warn(dev, "Failed to update vram location.\n");
 
-	hv->dirt_needed = true;
-
 	ret = hyperv_mode_config_init(hv);
 	if (ret)
 		goto err_free_mmio;