net: smsc911x: Fix runtime PM imbalance on error

commit 539d39ad upstream.

Remove runtime PM usage counter decrement when the
increment function has not been called to keep the
counter balanced.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>