ANDROID: usb: gadget: f_midi: rework cleanup path

An issue was found where a device is unable to switch USB mode after
selecting MIDI functionality. The userspace switch logic was found to be
different than expected, and therefore a complete device removal is not
appropriate for the disable case. Instead, implement an info clear
function to uninitialize the midi information during teardown, but do
not remove the android midi device until the f_midi instance is freed.

Steps to reproduce the original issue:
1. Connect the Android device via USB cable to the computer.
2. Open the USB Preference dialog box to change the USB function.
3. Select the MIDI function.
4. Select the MTP, PTP, or other desired USB function.
5. Wait a moment for the USB function UI to become inactive and unable to
switch.

Test: manually tested the above steps, and successfully switch between
USB modes.
Bug: 322732675
Bug: 120441124
Signed-off-by: Neill Kapron <nkapron@google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:d399811b2a58e0ade271ea9d1ef78f89c8926523)
Merged-In: Ie291e44ab5d6d194da6b488d0d2e533b9f3c538a
Change-Id: Ie291e44ab5d6d194da6b488d0d2e533b9f3c538a