net: No line break on netdev_WARN* formatting

Remove the unnecessary line break between the netdev name and reg state
to the actual message that should be printed.

For example, this:
[86730.307236] ------------[ cut here ]------------
[86730.313496] netdevice: enp27s0f0
Message from the driver
[...]

Will be replaced with:
[86770.259289] ------------[ cut here ]------------
[86770.265191] netdevice: enp27s0f0: Message from the driver
[...]

Signed-off-by: Gal Pressman <galp@mellanox.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>