Fix constant name for KEY_PICTURE_TYPE

Follow existing convention of using '-', instead of '_' for
a key name with multiple words.

Bug: 223084538
Test: CTS
Change-Id: I1375337286e6555b7a6b8f7d5ff0839ec790ff1a
diff --git a/media/libstagefright/include/media/stagefright/MediaCodecConstants.h b/media/libstagefright/include/media/stagefright/MediaCodecConstants.h
index fa9dc8b..9040e8b 100644
--- a/media/libstagefright/include/media/stagefright/MediaCodecConstants.h
+++ b/media/libstagefright/include/media/stagefright/MediaCodecConstants.h
@@ -815,7 +815,7 @@
 constexpr char KEY_OPERATING_RATE[] = "operating-rate";
 constexpr char KEY_OUTPUT_REORDER_DEPTH[] = "output-reorder-depth";
 constexpr char KEY_PCM_ENCODING[] = "pcm-encoding";
-constexpr char KEY_PICTURE_TYPE[] = "picture_type";
+constexpr char KEY_PICTURE_TYPE[] = "picture-type";
 constexpr char KEY_PIXEL_ASPECT_RATIO_HEIGHT[] = "sar-height";
 constexpr char KEY_PIXEL_ASPECT_RATIO_WIDTH[] = "sar-width";
 constexpr char KEY_PREPEND_HEADER_TO_SYNC_FRAMES[] = "prepend-sps-pps-to-idr-frames";