staging: rtl8188eu: remove unnecessary variable

We just want to check if rtw_usb_if1_init returns NULL, which means there
was an error.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210407170531.29356-7-martin@kaiser.cx


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