drm/panthor: Fix a couple -ENOMEM error codes

These error paths forgot to set the error code to -ENOMEM.

Fixes: 647810ec ("drm/panthor: Add the MMU/VM logical block")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/cf5bbba5-427e-4940-b91e-925f9fa71f8d@moroto.mountain