staging: r8188eu: Makefile: don't overwrite global settings

Remove settings from the Makefile that are set by higher-level Makefiles.

Some of those settings might have been useful when the driver was
maintained out of tree.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211016173544.25376-3-martin@kaiser.cx


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