Update android/input.h docs

Fix doc generation error

Bug: 183013620
Test: ./_scripts/update_api_doc.py ~/android/master/ 2>&1 >/dev/null | grep -i input

Before:
android/input.h:680: warning: unable to resolve link to `RELATIVE_X' for \link command
After:
the line above is not present

Change-Id: I995ac91d8bfd53309607e3cdac305adb68d40d78
diff --git a/include/android/input.h b/include/android/input.h
index 6fe95c0..bb98beb 100644
--- a/include/android/input.h
+++ b/include/android/input.h
@@ -678,7 +678,7 @@
     /**
      * Axis constant: The movement of y position of a motion event.
      *
-     * Same as {@link RELATIVE_X}, but for y position.
+     * Same as {@link AMOTION_EVENT_AXIS_RELATIVE_X}, but for y position.
      */
     AMOTION_EVENT_AXIS_RELATIVE_Y = 28,
     /**