compatibility_matrix: restore P graphics.composer

graphics.composer 2.3 was added in Android Q, so it is in the
compatibility matrix for target-level 4. Devices updating from P
to Q will automatically have this option applies. However, for
sanity, we try to keep the P compatibility matrix between releases.

This change should have no functional difference except minimizing
the delta in this file between P/Q branches.

Bug: 126892442
Test: diff compatibility matrix files
Test: these matrices are verified at build time
Change-Id: I8514c7b6ce4c2670ce7926fb31b09ed783d17dca
diff --git a/compatibility_matrices/compatibility_matrix.3.xml b/compatibility_matrices/compatibility_matrix.3.xml
index 4cb3776..e13d293 100644
--- a/compatibility_matrices/compatibility_matrix.3.xml
+++ b/compatibility_matrices/compatibility_matrix.3.xml
@@ -193,7 +193,7 @@
     </hal>
     <hal format="hidl" optional="false">
         <name>android.hardware.graphics.composer</name>
-        <version>2.1-3</version>
+        <version>2.1-2</version>
         <interface>
             <name>IComposer</name>
             <instance>default</instance>