w83792d: Fix unchecked return status

Fix the w83792d driver. Add error checking to device_create_file
and also care to destroy the files upon exit.
Signed-off-by: NRudolf Marek <r.marek@assembler.cz>
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>