drm/vmwgfx: Fix Host-Backed userspace on Guest-Backed kernel

Running 3D applications with SVGA_FORCE_HOST_BACKED=1 or using an
ancient version of mesa was broken because the buffer was pinned in
VMW_BO_DOMAIN_SYS and could not be moved to VMW_BO_DOMAIN_MOB during
validation.

The compat_shader buffer should not pinned.

Fixes: 668b206 ("drm/vmwgfx: Stop using raw ttm_buffer_object's")
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Reviewed-by: Maaz Mombasawala <maaz.mombasawala@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://lore.kernel.org/r/20250429203427.1742331-1-ian.forbes@broadcom.com

Author: en4bz

drivers/gpu/drm/vmwgfx/vmwgfx_shader.c

@@ -896,7 +896,7 @@ int vmw_compat_shader_add(struct vmw_private *dev_priv,
 		.busy_domain = VMW_BO_DOMAIN_SYS,
 		.bo_type = ttm_bo_type_device,
 		.size = size,
-		.pin = true,
+		.pin = false,
 		.keep_resv = true,
 	};