usb: gadget: Fix non-unique driver names in raw-gadget driver

In a report for a separate bug (which has already been fixed by commit
5f0b5f4d "usb: gadget: fix race when gadget driver register via
ioctl") in the raw-gadget driver, the syzbot console log included
error messages caused by attempted registration of a new driver with
the same name as an existing driver:

> kobject_add_internal failed for raw-gadget with -EEXIST, don't try to register things with the same name in the same directory.
> UDC core: USB Raw Gadget: driver registration failed: -17
> misc raw-gadget: fail, usb_gadget_register_driver returned -17

These errors arise because raw_gadget.c registers a separate UDC
driver for each of the UDC instances it creates, but these drivers all
have the same name: "raw-gadget".  Until recently this wasn't a
problem, but when the "gadget" bus was added and UDC drivers were
registered on this bus, it became possible for name conflicts to cause
the registrations to fail.  The reason is simply that the bus code in
the driver core uses the driver name as a sysfs directory name (e.g.,
/sys/bus/gadget/drivers/raw-gadget/), and you can't create two
directories with the same pathname.

To fix this problem, the driver names used by raw-gadget are made
distinct by appending a unique ID number: "raw-gadget.N", with a
different value of N for each driver instance.  And to avoid the
proliferation of error handling code in the raw_ioctl_init() routine,
the error return paths are refactored into the common pattern (goto
statements leading to cleanup code at the end of the routine).

Link: https://lore.kernel.org/all/0000000000008c664105dffae2eb@google.com/
Fixes: fc274c1e

 "USB: gadget: Add a new bus for gadgets"
CC: Andrey Konovalov <andreyknvl@gmail.com>
CC: <stable@vger.kernel.org>
Reported-and-tested-by:  <syzbot+02b16343704b3af1667e@syzkaller.appspotmail.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Acked-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/YqdG32w+3h8c1s7z@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>