w83l785ts: Fix unchecked return status

Fix the w83l785ts driver. Add error checking to device_create_file
and also care to destroy the files upon exit.
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>