usb: ulpi: Fix debugfs directory leak

The ULPI per-device debugfs root is named after the ulpi device's
parent, but ulpi_unregister_interface tries to remove a debugfs
directory named after the ulpi device itself. This results in the
directory sticking around and preventing subsequent (deferred) probes
from succeeding. Change the directory name to match the ulpi device.

Fixes: bd0a0a02

 ("usb: ulpi: Add debugfs support")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20240126223800.2864613-1-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>