Enable mounting of connected USB storage devices:

Thanks to CyanogenMod:
https://github.com/CyanogenMod/android_device_asus_flo/commit/b9b1f770c1d2a7ea9106c901f3f1eac3e3f735a2
https://github.com/CyanogenMod/android_device_asus_flo/commit/4a0f112e22f5118787d6b6ce0d777259161350e2