staging: rtl8192u: fix open brace position in r819xU_cmdpkt.h

This patch fixes the following checkpatch warning and error:
WARNING: missing space after enum definition
ERROR: open brace '{' following enum go on the same line

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