ctcm: replace sscanf by kstrto function

Since a single integer value is read from the supplied buffer
use the kstrto functions instead of sscanf.

Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>