libata: make ata_port_type const

Make this const as it is only stored in the const field of a device
structure. Make the declaration in header const too.

Structure found using Coccinelle and changes done by hand.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 65f7574..29e3516 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -5824,7 +5824,7 @@ void ata_host_resume(struct ata_host *host)
 }
 #endif
 
-struct device_type ata_port_type = {
+const struct device_type ata_port_type = {
 	.name = "ata_port",
 #ifdef CONFIG_PM
 	.pm = &ata_port_pm_ops,