staging: rtl8188eu: ctrl vendor req index is not used

The index for rtl8188eu's vendor-specific control requests is not used.
Remove the index parameter from usbctrl_vendorreq and pass index 0 to
usb_control_msg.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210406204829.18130-3-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>