usbnet: smsc95xx: fix memory leak in smsc95xx_suspend

This patch fixes memory leak in smsc95xx_suspend.

Also, it isn't necessary to bother mm to allocate 8bytes/16byte,
and we can use stack variable safely.

Acked-By: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>