fix error detected by code inspeaction

view.php

@@ -40,7 +40,7 @@ if ($id) {
     $book = $DB->get_record('book', array('id'=>$cm->instance), '*', MUST_EXIST);
 } else {
     $book = $DB->get_record('book', array('id'=>$bid), '*', MUST_EXIST);
-    $cm = get_coursemodule_from_instance('book', $book->id, 0, false, MU<ST_EXIST);
+    $cm = get_coursemodule_from_instance('book', $book->id, 0, false, MUST_EXIST);
     $course = $DB->get_record('course', array('id'=>$cm->course), '*', MUST_EXIST);
     $id = $cm->id;
 }