usb: gadget: Remove superfluous name casts

device_driver.name is "const char *"

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>