update xtrx images git hash

Build failed due to a submodule that was removed.
Flatpak 1.4.1 cannot sort this out correctly.

flatpak/org.sdrangel.SDRangel.json

@@ -216,7 +216,7 @@
         {
           "type": "git",
           "url": "https://github.com/xtrx-sdr/images.git",
-          "commit": "053ec82"
+          "commit": "9586a6e"
         }
       ]
     },