UPSTREAM: net: usbnet: Fix -Wcast-function-type

correct usage prototype of callback in tasklet_init().
Report by https://github.com/KSPP/linux/issues/20



Signed-off-by: Phong Tran <tranmanphong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 2eb1d3f4bcae6c83943214ccb26968a48360db06)
Bug: 147506196
Change-Id: Ia9d7fe3e8118c2570ae037645e259082bd813222
Signed-off-by: Alistair Delva <adelva@google.com>