staging: r8188eu: os_dep: remove unused static variable

Remove unused static variable rtw_enusbss from os_intfs.c file.

Acked-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Link: https://lore.kernel.org/r/YSoz5Qip12K899SN@user


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