floppy: fix calling platform_device_unregister() on invalid drives

floppy: fix calling platform_device_unregister() on invalid drives

platform_device_unregister() should only be called when
a respective platform_device_register() is called. However
the floppy driver currently allows failures when registring
a drive and a bail out could easily cause an invalid call
to platform_device_unregister() where it was not intended.

Fix this by adding a bool to keep track of when the platform
device was registered for a drive.

This does not fix any known panic / bug. This issue was found
through code inspection while preparing the driver to use the
up and coming support for device_add_disk() error handling.
From what I can tell from code inspection, chances of this
ever happening should be insanely small, perhaps OOM.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20210927220302.1073499-5-mcgrof@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>