cxgb4/cxgb4vf: Use fl capacity to check if fl needs to be replenished

Use freelist capacity instead of freelist size while checking, if
freelist needs to be refilled

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>