can: ti_hecc: Fix napi poll return value for repoll

After commit d75b1ade ("net: less interrupt masking in NAPI") napi
repoll is done only when work_done == budget.
So we need to return budget if there are still packets to receive.

Signed-off-by: Oliver Stäbler <oliver.staebler@bytesatwork.ch>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>