USB: dummy-hcd: use dynamic allocation for platform_devices

This patch (as1075) changes dummy-hcd to dynamically allocate its
platform_device structures, using the core platform_device_alloc()
interface.  This is what it should have done all along, because the
dynamically-allocated structures have a release method in the driver
core and are therefore immune to being released after the module has
been unloaded.

Thanks to Richard Purdie for pointing out the need for this change.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>