Add strongbox KM instance to compatibilty matrix

Test: builds
Bug: 68112778
Change-Id: If04ff2b5ab95dd1a17c145f509657e5438d00bdc
diff --git a/compatibility_matrices/compatibility_matrix.current.xml b/compatibility_matrices/compatibility_matrix.current.xml
index 61a6608..b500ed4 100644
--- a/compatibility_matrices/compatibility_matrix.current.xml
+++ b/compatibility_matrices/compatibility_matrix.current.xml
@@ -182,7 +182,7 @@
         <interface>
             <name>IKeymasterDevice</name>
             <instance>default</instance>
-	    <!-- TODO: strongbox here? -->
+            <instance>strongbox</instance>
         </interface>
     </hal>
     <hal format="hidl" optional="true">