usb: gadget: legacy: fix error return code in gncm_bind()

commit e27d4b30b71c66986196d8a1eb93cba9f602904a upstream.

If 'usb_otg_descriptor_alloc()' fails, we must return a
negative error code -ENOMEM, not 0.

Fixes: 1156e91d ("usb: gadget: ncm: allocate and init otg descriptor by otg capabilities")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>