Use mass_storage also as fake charging mode with android gadget

Seems an empty android gadget only enumerates if some configuration had
been used before. Fix this by using mass_storage to make a similar fake
mass_storage device as used with normal modules.

[usb-moded] Use fake mass_storage for android gadget charging mode. Fixes: JB#8277

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>

src/usb_moded-android.c

@@ -89,9 +89,9 @@ int set_android_charging_mode(void)
 {
    int ret = 0;
 
-   /* disable, set functions to "null", re-enable */
+   /* disable, set functions to "mass_storage", re-enable */
    write_to_file("/sys/class/android_usb/android0/enable", "0");
-   write_to_file("/sys/class/android_usb/android0/functions", "null");
+   write_to_file("/sys/class/android_usb/android0/functions", "mass_storage");
    ret = write_to_file("/sys/class/android_usb/android0/enable", "1");
    if(ret < 0)
 	return(1);