ImageReader: fix missing pixel stride

Change-Id: Ie34cb51fee90e2d5624663fa23da4093fec435e2
diff --git a/media/jni/android_media_ImageReader.cpp b/media/jni/android_media_ImageReader.cpp
index 1c043e0..4ac62f5 100644
--- a/media/jni/android_media_ImageReader.cpp
+++ b/media/jni/android_media_ImageReader.cpp
@@ -574,6 +574,7 @@
         case HAL_PIXEL_FORMAT_Y8:
             // Single plane 8bpp data.
             ALOG_ASSERT(idx == 0, "Wrong index: %d", idx);
+            pixelStride = 1;
             break;
         case HAL_PIXEL_FORMAT_YV12:
             pixelStride = 1;