staging: rtl8188eu: remove RT_TRACE prints from usb_intf.c

Eventually, all driver-specific debug prints should be removed.
Take another step in that direction.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210620175301.14988-2-martin@kaiser.cx


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