staging: r8188eu: remove null pointer checks before kfree

kfree(NULL) is safe, so remove unnecessary null pointer checks before
calls to kfree. Reported by checkpatch.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210818085809.31451-1-straube.linux@gmail.com


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