staging: ozwpan: Fix crash for race condition.

Do not allocate a port to new device or process URB when its status is
yet to be read. This avoids race condition when USB core read hub
status a bit late, while new device tries to acquire port.

Signed-off-by: Rupesh Gujare <rupesh.gujare@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>