fix API description on how to round average qp

Average QP is rounded to the nearest integer value.

Test: cts
Bug: 229778486
Change-Id: I16fca81dcab26462b9493784368d29c6b7748fd5

media/java/android/media/MediaFormat.java

@@ -1147,7 +1147,7 @@ public final class MediaFormat {
      * A key describing the per-frame average block QP (Quantization Parameter).
      * This is a part of a video 'Encoding Statistics' export feature.
      * This value is emitted from video encoder for a video frame.
-     * The average value is rounded down (using floor()) to integer value.
+     * The average value is rounded to the nearest integer value.
      *
      * The associated value is an integer.
      */