staging: rtl8723bs: fix typo in the TODO file

HGz -> GHz
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/TODO

 TODO:
 - find and remove code blocks guarded by never set CONFIG_FOO defines
-- find and remove remaining code valid only for 5 HGz. Most of the obvious
+- find and remove remaining code valid only for 5 GHz. Most of the obvious
   ones have been removed, but things like channel > 14 still exist.
 - find and remove any code for other chips that is left over
 - convert any remaining unusual variable types