net: bridge: fix ioctl old_deviceless bridge argument

Commit ad2f99ae ("net: bridge: move bridge ioctls out of .ndo_do_ioctl")
changed the source of the argument copy in bridge's old_deviceless() from
args[1] (user ptr to device name) to uarg (ptr to ioctl arguments) causing
wrong device name to be used.

Example (broken, bridge exists but is up):
$ brctl delbr bridge
bridge bridge doesn't exist; can't delete it

Example (working):
$ brctl delbr bridge
bridge bridge is still up; can't delete it

Fixes: ad2f99ae

 ("net: bridge: move bridge ioctls out of .ndo_do_ioctl")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>