usb: gadget: Fix memleak in gadgetfs_fill_super

usb: gadget: Fix memleak in gadgetfs_fill_super

usb_get_gadget_udc_name will alloc memory for CHIP
in "Enomem" branch. we should free it before error
returns to prevent memleak.

Fixes: d6a267c618f13 ("usb: gadget: provide interface for legacy gadgets to get UDC name")
Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Link: https://lore.kernel.org/r/20201117021629.1470544-3-zhangqilong3@huawei.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>