cxgb3: fix device opening error path

Only negative return from bind_qsets() should be considered an error and
propagated.
It fixes an issue reported by IBM on P Series platform.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Tested-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>