pch_can: fix module reload issue with MSI

Currently, in case reload pch_can,
pch_can not to be able to catch interrupt.

The cause is bus-master is not set in pch_can.
Thus, add enabling bus-master processing.

Signed-off-by: Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
Signed-off-by: David S. Miller <davem@davemloft.net>