net/mlx4_core: Fix error handling in mlx4_init_port_info.

Avoid exiting the function with a lingering sysfs file (if the first
call to device_create_file() fails while the second succeeds), and avoid
calling devlink_port_unregister() twice.

In other words, either mlx4_init_port_info() succeeds and returns zero, or
it fails, returns non-zero, and requires no cleanup.

Fixes: 096335b3 ("mlx4_core: Allow dynamic MTU configuration for IB ports")
Signed-off-by: Tarick Bedeir <tarick@google.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>