rtl8192u: fix whitespace around if statements in r8192U.h

This patch fixes a part of the following checkpatch error:
ERROR: space required before the open parenthesis '('
by adding space after if

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