[NET]: Fix yam.c

drivers/net/hamradio/yam.c: In function `yam_tx_byte':
drivers/net/hamradio/yam.c:643: warning: passing arg 1 of `skb_copy_from_linear_data_offset' from incompatible pointer type

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>