can: c_can: Update D_CAN TX and RX functions to 32 bit - fix Altera Cyclone access

When testing CAN write floods on Altera's CycloneV, the first 2 bytes
are sometimes 0x00, 0x00 or corrupted instead of the values sent. Also
observed bytes 4 & 5 were corrupted in some cases.

The D_CAN Data registers are 32 bits and changing from 16 bit writes to
32 bit writes fixes the problem.

Testing performed on Altera CycloneV (D_CAN).  Requesting tests on other
C_CAN & D_CAN platforms.

Reported-by: Richard Andrysek <richard.andrysek@gomtec.de>
Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>