can: c_can: fix invalid error codes

Errors in CAN protocol (location) are reported in data[3] of the can
frame instead of data[2].

Cc: linux-stable <stable@vger.kernel.org>
Cc: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: Olivier Sobrie <olivier@sobrie.be>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>