rtl8192u: fix whitespace around ~ in r8180_93cx6.c

This patch fixes the whitespace around ~ and corrects the
following checkpatch error:
ERROR: space prohibited after that '~'

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>