firmware: vpd: Fix platform driver and device registration/unregistration

The driver exit function needs to unregister both platform device and
driver. Also, during registration, register driver first and perform
error checks.

Fixes: 049a59db ("firmware: Google VPD sysfs driver")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable <stable@vger.kernel.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>