usb: android: Fix crash on composition switch from ncm

On composition switch from a ncm composition to any other
composition below call stack is seen

[<ffffffc00031cc1c>] __list_del_entry+0x74/0xd8
[<ffffffc00031cc90>] list_del+0x10/0x38
[<ffffffc000641154>] usb_remove_function+0x34/0x58
[<ffffffc000673330>] ncm_function_unbind_config+0x1c/0x28
[<ffffffc00067424c>] android_unbind_config+0x4c/0x70
[<ffffffc000642200>] unbind_config.isra.8+0xd0/0xec
[<ffffffc000643984>] usb_remove_config+0x80/0x94
[<ffffffc000672eb8>] android_disable+0x74/0x94
[<ffffffc000673054>] enable_store+0x17c/0x250
[<ffffffc000500400>] dev_attr_store+0x1c/0x28
[<ffffffc0001fe0d4>] sysfs_kf_write+0x40/0x4c
[<ffffffc0001fd3fc>] kernfs_fop_write+0xfc/0x144
[<ffffffc00019f298>] vfs_write+0xb8/0x194

unbind_config() extracts each member from the functions list and calls
unbind_config() callback of that particular function driver. Also before
calling the unbind() callback it deletes this function from the function
list.
ncm_function_unbind_config() calls usb_remove_function() which again tries
to delete the ncm function from the function list and this leads to a
crash.
Fix this by instantiating the ncm function in ncm_function_bind_config()
and de-instantiating in ncm_function_unbind_config().

Change-Id: I649e36e3b48b5db1795cd37edff3af25a6330450
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>