staging:ozwpan: Fix following warning.

The patch ae926051: "staging: ozwpan: Added USB HCD
implementation" from Feb 20, 2012, leads to the following warning:
drivers/staging/ozwpan/ozhcd.c:1094 oz_hcd_heartbeat()
	 warn: what is this condition about? 'ep->buffered_units * 50'

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rupesh Gujare <rupesh.gujare@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>