staging:rtl8192u: Add spaces around '+' operator - Style

Add spaces around '+' operator as required by the coding standard.
This clears the checkpatch issue.

This change is purely coding style in nature and should have not
effect on runtime code execution.

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