[Coverity 1666178] Same on both sides CSSGrammar.y

This is often the result of a copy and paste error. It may result in the operator always evaluating to the same result.

In cssparse: The same expression occurs on both sides of an operator. (CWE-1025)

438    | '[' maybe_space attr_name match maybe_space ident_or_string maybe_space ']' {
439        $$ = vlc_css_selector_New( SPECIFIER_ATTRIB, $3 );
     
CID 1666178: (#1 of 1): Same on both sides (CONSTANT_EXPRESSION_RESULT)
pointless_expression: The expression yyval.selector && yyval.selector does not accomplish anything because it evaluates to either of its identical operands, yyval.selector.
      Did you intend the operands to be different?
440        if( $$ && $$ )
441        {
442            $$->match = $4;
443            $$->p_matchsel = vlc_css_selector_New( SPECIFIER_ID, $6 );
444        }

Likely bogus copy paste in 3a6dd613