staging:rtl8192u: Rename enum DIRECTION_VALUE - Style

The enumerated type DIRECTION_VALUE should be named in lowercase to
comply with coding standard so is renamed to direction_value. In
addition the 'typedef' directive has been removed to clear the
checkpatch issue with defining new types.

These changes are coding style changes which should have no impact on
runtime code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>