staging: vt6656: parse cts fall back out of vnt_fill_cts_head

Creating new function vnt_fill_cts_fb_head for the fall back rates.

The check for fb_option is now done in vnt_rxtx_cts.

This fixes checkpatch warning
WARNING: else is not generally useful after a break or return
	559: FILE: drivers/staging/vt6656/rxtx.c:559:

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>