Drive logic when testing performance

src/freedombone-controlpanel

@@ -1811,8 +1811,12 @@ function performance_benchmarks {
     fi
 
     test_drive=/dev/sda1
-    if ls /dev/mmcblk0p2; then
-        test_drive=/dev/mmcblk0p2
+    if ! ls $test_drive; then
+        if ls /dev/mmcblk0p2; then
+            test_drive=/dev/mmcblk0p2
+        else
+            return
+        fi
     fi
     clear
     echo ''