microsd device name for performance check

src/freedombone-controlpanel

@@ -1812,8 +1812,8 @@ function performance_benchmarks {
     fi
 
     test_drive=/dev/sda1
-    if [ -f /dev/mmcblk0 ]; then
-        test_drive=/dev/mmcblk0
+    if [ -f /dev/mmcblk0p2 ]; then
+        test_drive=/dev/mmcblk0p2
     fi
     echo ''
     echo $"Testing read speed of drive $test_drive"