Commit d3cd1565 introduced a bug, the
interrupt handler would loop endlessly if the CANINTF_MERRF bit is set,
because it's not cleared.

This patch fixes the problem by masking out the CANINTF_MERRF and all other
non interesting bits.
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>