usb: gadget: remove leaked entry from udc driver list

The usb_add_gadget_udc will add a new gadget to the udc class
driver list. Not calling usb_del_gadget_udc in error branch
will result in residual gadget entry in the udc driver list.
We fix it by calling usb_del_gadget_udc to clean it when error
return.

Fixes: 48ba02b2

 ("usb: gadget: add udc driver for max3420")
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Link: https://lore.kernel.org/r/20210727073142.84666-1-zhangqilong3@huawei.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>