um: vector: Use GFP_ATOMIC under spin lock

Use GFP_ATOMIC instead of GFP_KERNEL under spin lock to fix possible
sleep-in-atomic-context bugs.

Fixes: 9807019a ("um: Loadable BPF "Firmware" for vector drivers")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>