staging: r8188eu: Remove set but unused variables

Remove set but unused variables. Issues detected by sparse.

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20210802010056.20543-1-fmdefrancesco@gmail.com


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