fix(input): use the right ID for the label. (#515)

Fixes #512.

Author: hansl

src/components/input/input.html

@@ -34,7 +34,7 @@
              (change)="handleChange($event)">
 
       <label class="md-input-placeholder"
-             [attr.for]="id"
+             [attr.for]="inputId"
              [class.md-empty]="empty"
              [class.md-focused]="focused"
              [class.md-float]="floatingPlaceholder"