can: c_can: don't indicate triple sampling support for D_CAN

The D_CAN controller doesn't provide a triple sampling mode, so don't set
the CAN_CTRLMODE_3_SAMPLES flag in ctrlmode_supported. Currently enabling
triple sampling is a no-op.

Signed-off-by: Richard Schütz <rschuetz@uni-koblenz.de>
Cc: linux-stable <stable@vger.kernel.org> # >= v3.6
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>