can: grcan: only use the NAPI poll budget for RX

can: grcan: only use the NAPI poll budget for RX

The previous split budget between TX and RX made it return not using
the entire budget but at the same time not having calling called
napi_complete. This sometimes led to the poll to not be called, and at
the same time having TX and RX interrupts disabled resulting in the
driver getting stuck.

Fixes: 6cec9b07fe6a ("can: grcan: Add device driver for GRCAN and GRHCAN cores")
Link: https://lore.kernel.org/all/20220429084656.29788-4-andreas@gaisler.com
Cc: stable@vger.kernel.org
Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>