USB: gadget: lpc32xx_udc: remove debugfs dentry variable

USB: gadget: lpc32xx_udc: remove debugfs dentry variable

There is no need to store the dentry for a fixed filename that we have
the string for.  So just have debugfs look it up when we need it to
remove the file, no need to store it anywhere locally.

Note, this driver is broken in that debugfs will not work for more than
one instance of the device it supports.  But given that this patch does
not change that, and no one has ever seemed to notice, it must not be an
issue...

Cc: Felipe Balbi <balbi@kernel.org>
Cc: Vladimir Zapolskiy <vz@mleia.com>
Cc: linux-usb@vger.kernel.org
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Link: https://lore.kernel.org/r/20210518162035.3697860-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>