net: socionext: replace napi_alloc_frag with the netdev variant on init

The netdev variant is usable on any context since it disables interrupts.
The napi variant of the call should only be used within softirq context.
Replace napi_alloc_frag on driver init with the correct netdev_alloc_frag
call

Changes since v1:
- Adjusted commit message

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Jassi Brar <jaswinder.singh@linaro.org>
Fixes: 4acb20b4

 ("net: socionext: different approach on DMA")
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>