tc35815: Fix build error if NAPI enabled

This driver contains experimental NAPI code disabled by default.
The commit bea3348e

 ("[NET]: Make NAPI polling independent of struct
net_device objects.") converted the NAPI path of this driver but that
conversion was not complete.  This patch fixes a build error
introduced by the commit.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>