Use correct sizeof operand in qsort call

Probably no practical impact, since all pointers ought to have the
same size, but it was wrong nonetheless.  Found by Coverity.

Author: petere

src/backend/utils/adt/tsrank.c

@@ -175,7 +175,7 @@ SortAndUniqItems(TSQuery q, int *size)
 	if (*size < 2)
 		return res;
 
-	qsort_arg(res, *size, sizeof(QueryOperand **), compareQueryOperand, (void *) operand);
+	qsort_arg(res, *size, sizeof(QueryOperand *), compareQueryOperand, (void *) operand);
 
 	ptr = res + 1;
 	prevptr = res;