staging: ft1000: Rename ft1000_chdev.c to ft1000_debug.c.

Name of old file was misleading because it is currently
updated to debugfs so change also file name.

Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>