In the Linux kernel, the following vulnerability has been resolved: usb: gadget: midi2: remove default configfs groups on teardown f_midi2

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: midi2: remove default configfs groups on teardown

f_midi2_alloc_inst() creates default configfs child groups for the
default endpoint and default block using configfs_add_default_group(),
setting their internal refcount to 1.

However, during function teardown in f_midi2_free_inst() or EP cleanup
in f_midi2_ep_opts_release(), configfs_remove_default_groups() is
never called, therefore never dropping the refcount and leaking struct
f_midi2_ep_opts and f_midi2_block_opts.

Add the missing configfs_remove_default_groups() in the afformentioned
functions to free the structs properly.