docs(mdDialog): update controller docs

Closes #1449

Author: Marcy Sutton

src/components/dialog/dialog.js

@@ -76,11 +76,12 @@ function MdDialogDirective($$rAF, $mdTheming) {
  *   function AppController($scope, $mdDialog) {
  *     var alert;
  *     $scope.showAlert = showAlert;
+ *     $scope.showDialog = showDialog;
  *     $scope.items = [1, 2, 3];
  *
  *     // Internal method
  *     function showAlert() {
- *       var alert = $mdDialog.alert({
+ *       alert = $mdDialog.alert({
  *         title: 'Attention',
  *         content: 'This is an example of how easy dialogs can be!',
  *         ok: 'Close'
@@ -283,7 +284,7 @@ function MdDialogDirective($$rAF, $mdTheming) {
  *   - `escapeToClose` - `{boolean=}`: Whether the user can press escape to close the dialog.
  *     Default true.
  *   - `controller` - `{string=}`: The controller to associate with the dialog. The controller
- *     will be injected with the local `$hideDialog`, which is a function used to hide the dialog.
+ *     will be injected with the local `$mdDialog`, which passes along a scope for the dialog.
  *   - `locals` - `{object=}`: An object containing key/value pairs. The keys will be used as names
  *     of values to inject into the controller. For example, `locals: {three: 3}` would inject
  *     `three` into the controller, with the value 3. If `bindToController` is true, they will be