PCI: keystone: Do not treat link up message as error

The "Link already up" message does not indicate any error, so
change it to dev_info() level instead.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Murali Karicheri <m-karicheri2@ti.com>