migration: Remove MigrationState from migration_in_postcopy

We need to call for the migrate_get_current() in more that half of the
uses, so call that inside.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
diff --git a/migration/migration.c b/migration/migration.c
index 2990c40..7da16cf 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1062,14 +1062,16 @@
             s->state == MIGRATION_STATUS_FAILED);
 }
 
-bool migration_in_postcopy(MigrationState *s)
+bool migration_in_postcopy(void)
 {
+    MigrationState *s = migrate_get_current();
+
     return (s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE);
 }
 
 bool migration_in_postcopy_after_devices(MigrationState *s)
 {
-    return migration_in_postcopy(s) && s->postcopy_after_devices;
+    return migration_in_postcopy() && s->postcopy_after_devices;
 }
 
 bool migration_is_idle(MigrationState *s)