staging: r8188eu: remove unused bitshift function

The bitshift function from osdep_service.h is not used.
Remove it.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220115165536.231210-4-martin@kaiser.cx


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