[ldv-project] ipw2x00: add checks for dma mapping errors

[Kalle Valo]

> ipw2100_alloc_skb() and ipw2100_tx_send_data() do not check if mapping
> dma memory succeed. The patch adds the checks and failure handling.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Alexey Khoroshilov <khoroshilov at ispras.ru>

Thanks, applied to wireless-drivers-next.git.

Kalle Valo