atm: iphase: remove redundant pointer skb

The pointer skb is redundant, it is assigned a value that is never
read and hence can be removed. Cleans up clang scan warning:

drivers/atm/iphase.c:205:18: warning: Although the value stored
to 'skb' is used in the enclosing expression, the value is never
actually read from 'skb' [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>