staging: rtl8188eu: add spaces around '+' in usb_halinit.c

Add spaces around '+' to improve readability and follow kernel
coding style. Reported by checkpatch.
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Link: https://lore.kernel.org/r/20190726180448.2290-1-straube.linux@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>