ozwpan: replace alloc_skb with dev_alloc_skb in ozpd.c

This patch replaces the calls to alloc_skb with calls
to dev_alloc_skb.

dev_alloc_skb has GFP_ATOMIC priority so the
replacement does not change the code semantics.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>