driver core: platform: Respect return code of platform_device_register_full()

The platform_device_register_full() might return an error pointer. If we
instantiate platform device which is optional we may simplify the routine at
removal stage by simply calling platform_device_unregister(). For now it
requires to check parameter for being an error pointer in each caller.

To make users' life easier, check for an error pointer inside driver core.

Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>