compatibility_matrices: Allow radio 1.5 on target-level 6

* I do expect 1.5 support will get deprecated in framework, the
  purpose of this is for Radio HIDL->AIDL wrapper to use

Change-Id: I5baf60d94affef649d68ef3f076539e04221ed41

Author: me-cafebabe

compatibility_matrices/compatibility_matrix.6.xml

@@ -450,7 +450,7 @@
     </hal>
     <hal format="hidl">
         <name>android.hardware.radio</name>
-        <version>1.6</version>
+        <version>1.5-6</version>
         <interface>
             <name>IRadio</name>
             <instance>slot1</instance>