cxgb4: fix memory leak during module unload

Fix the memory leak in mps during module unload
path by freeing mps reference entries if the list
adpter->mps_ref is not already empty

Fixes: 28b38705 ("cxgb4: Re-work the logic for mps refcounting")
Signed-off-by: Raju Rangoju <rajur@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>