devlink: Make port index data type as unsigned int

Devlink port index attribute is returned to users as u32 through
netlink response.
Change index data type from 'unsigned' to 'unsigned int' to avoid
below checkpatch.pl warning.

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
81: FILE: include/net/devlink.h:81:
+       unsigned index;

Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>