610281 - fix coverity Defect Type: Control flow issues
    
    https://bugzilla.redhat.com/show_bug.cgi?id=610281
    
    11794 DEADCODE Triaged Unassigned Bug Minor Ignore
    slapi_dn_syntax_check() ds/ldap/servers/slapd/plugin_syntax.c
    
    Comment:
    Checking for the possibility of dn == NULL is not needed
    since it is already checked at the line 303.