USB: fix interface sysfs file-creation bug

This patch (as1005) fixes a rather subtle problem.  When
usb_set_configuration() registers the interfaces and their files in
sysfs, it doesn't expect those files to exist already.  But when an
interface is registered, its driver may call usb_set_interface() and
thereby cause the sysfs files to be created.  The result is an error
when usb_set_configuration() goes on to create those same files again.

The (not-so-great) solution is to have usb_set_configuration() remove
any existing files before creating them.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>