LibVideo: Fix two comment typos

Userland/Libraries/LibVideo/Containers/Matroska/Reader.cpp

@@ -557,7 +557,7 @@ static DecoderErrorOr<Block> parse_simple_block(Streamer& streamer, Time cluster
     //     timestamp of a Block or SimpleBlock in nanoseconds you have to use the following formula:
     //         `( Cluster\Timestamp + ( block timestamp * TrackTimestampScale ) ) * TimestampScale`
     //
-    //     When a CodecDelay Element is set, its value MUST be substracted from each Block timestamp
+    //     When a CodecDelay Element is set, its value MUST be subtracted from each Block timestamp
     //     of that track. To get the timestamp in nanoseconds of the first frame in a Block or
     //     SimpleBlock, the formula becomes:
     //         `( ( Cluster\Timestamp + ( block timestamp * TrackTimestampScale ) ) * TimestampScale ) - CodecDelay`

Userland/Libraries/LibVideo/VP9/ContextStorage.h

@@ -212,7 +212,7 @@ struct FrameBlockContext {
     u8 segment_id { 0 };
 };
 
-// Block context that is kept between frames until explictly cleared.
+// Block context that is kept between frames until explicitly cleared.
 struct PersistentBlockContext {
     PersistentBlockContext()
         : available(false)