Silence non-clickable imagebutton

Change-Id: I1d00d86e1dd1ca2ebaa20cdee74f9f93a7581d9a
Fixes: 34710523
Test: turn on talkback and try to select button
diff --git a/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogImpl.java b/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogImpl.java
index 697cac9..b8b046b 100644
--- a/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogImpl.java
+++ b/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogImpl.java
@@ -433,7 +433,7 @@
                 return false;
             }
         });
-        row.icon = (ImageButton) row.view.findViewById(R.id.volume_row_icon);
+        row.icon = row.view.findViewById(R.id.volume_row_icon);
         row.icon.setImageResource(iconRes);
         if (row.stream != AudioSystem.STREAM_ACCESSIBILITY) {
             row.icon.setOnClickListener(new OnClickListener() {
@@ -465,6 +465,8 @@
                     row.userAttempt = 0;  // reset the grace period, slider updates immediately
                 }
             });
+        } else {
+            row.icon.setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_NO);
         }
     }