staging: rtl8188eu: Removed code valid for 5GHz

This patch removes support for channels > 14. That is from the TODO which
says:

	-find and remove remaining code valid only for 5HGz. Most of
	obvious ones have been removed, but things like channel > 14 still
	exist.

Signed-off-by: Bhaskar Singh <bhaskar.kernel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>