libata-eh.c: local functions should not be exposed globally

The function ata_ering_clear_cb is only referenced in this file and
should be marked static to prevent it from being exposed globally.

This quiets the sparse warning:

warning: symbol 'ata_ering_clear_cb' was not declared. Should it be static?
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-eh.c

@@ -419,7 +419,7 @@ int ata_ering_map(struct ata_ering *ering,
 	return rc;
 }
 
-int ata_ering_clear_cb(struct ata_ering_entry *ent, void *void_arg)
+static int ata_ering_clear_cb(struct ata_ering_entry *ent, void *void_arg)
 {
 	ent->eflags |= ATA_EFLAG_OLD_ER;
 	return 0;