usb: dwc3: use proper function for setting endpoint name

It's wrong to use the size of array as an argument for strncat.
Memory corruption is possible. strlcat is exactly what we need here.

Cc: stable@vger.kernel.org
Signed-off-by: Anton Tikhomirov <av.tikhomirov@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>