'ftdi' is alloced when probe device, but not free on device disconnect,
this cause a memory leak as follows:

unreferenced object 0xffff88800d584000 (size 8400):
  comm "kworker/0:2", pid 3809, jiffies 4295453055 (age 13.784s)
  hex dump (first 32 bytes):
    00 40 58 0d 80 88 ff ff 00 40 58 0d 80 88 ff ff  .@X......@X.....
    00 00 00 00 00 00 00 00 00 00 00 00 ad 4e ad de  .............N..
  backtrace:
    [<000000000d47f947>] kmalloc_order_trace+0x19/0x110 mm/slab_common.c:960
    [<000000008548ac68>] ftdi_elan_probe+0x8c/0x880 drivers/usb/misc/ftdi-elan.c:2647
    [<000000007f73e422>] usb_probe_interface+0x31b/0x800 drivers/usb/core/driver.c:396
    [<00000000fe8d07fc>] really_probe+0x299/0xc30 drivers/base/dd.c:517
    [<0000000005da7d32>] __driver_probe_device+0x357/0x500 drivers/base/dd.c:751
    [<000000003c2c9579>] driver_probe_device+0x4e/0x140 drivers/base/dd.c:781

Fix it by freeing 'ftdi' after nobody use it.

Fixes: a5c66e4b ("USB: ftdi-elan: client driver for ELAN Uxxx adapters")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20211217083428.2441-1-weiyongjun1@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>