staging: r8188eu: ctrl vendor req index is not used

staging: r8188eu: ctrl vendor req index is not used

The index for r8188eu's vendor-specific control requests is not used.
Remove the index parameter from usbctrl_vendorreq and pass index 0 to
usb_control_msg.

This patch is an adaptation of commit 3d0be94f62fd ("staging: rtl8188eu:
ctrl vendor req index is not used") for the new r8188eu driver.

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210818200041.10870-2-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>