staging: rtl8712: fixed no space coding style issue

Added space around the binary operator for readability in
rtl8712_xmit.h file

Signed-off-by: Selvakumar Elangovan <selvakumar16197@gmail.com>
Link: https://lore.kernel.org/r/20210309142547.16974-1-selvakumar16197@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>