usb: gadget: configs: plug memory leak

[ Upstream commit 38355b2a ]

When binding a gadget to a device, "name" is stored in gi->udc_name, but
this does not happen when unregistering and the string is leaked.

Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>