[SCSI] fusion: ensure NUL-termination of MptCallbacksName elements

Using strlcpy instead of memcpy makes the strlen() calls superfluous
and also ensures zero-termination of the copied string.
At the same time get rid of the magic constant 50.

Actually, I can't see why copying the callback name is necessary
instead of simply storing a pointer to it (just like to the callback
function itself), but that goes beyond the scope of this fix.

Signed-off-by: Ferenc Wagner <wferi@niif.hu>
Acked-by: "Nandigama, Nagalakshmi" <Nagalakshmi.Nandigama@lsi.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>