lpfc: fix missing zero termination in debugfs

If you feed 32 bytes in then the kstrtoull() doesn't receive a terminated
string so will run off the end.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>