staging: rtl8188eu: Fix spelling mistake

This patch fix spelling mistakes in TODO.
Signed-off-by: Bhaskar Singh <bhaskar.kernel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/TODO

 TODO:
-- 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