mscan: too much data copied to CAN frame due to 16 bit accesses

Due to the 16 bit access to mscan registers there's too much data copied to
the zero initialized CAN frame when having an odd number of bytes to copy.
This patch ensures that only the requested bytes are copied by using an
8 bit access for the remaining byte.

Reported-by: Andre Naujoks <nautsch@gmail.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>