MAINTAINERS: Update for migrated migration code

My previous patches migrated the migration code into migration/
but didn't update MAINTAINERS.

Note that does mean that the owner for block-migration.c
changes, but I'll ask block people what they want to do.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index d2f4a11..d72d6e3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -939,10 +939,9 @@
 M: Amit Shah <amit.shah@redhat.com>
 S: Maintained
 F: include/migration/
-F: migration*
+F: migration/
 F: savevm.c
 F: arch_init.c
-F: vmstate.c
 F: scripts/vmstate-static-checker.py
 F: tests/vmstate-static-checker-data/