can: sun4i: fix loopback mode

commit 3a379f5b36ae039dfeb6f73316e47ab1af4945df upstream.

Fix loopback mode by setting the right flag and remove presume mode.

Signed-off-by: Gerhard Bertelsmann <info@gerhard-bertelsmann.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>