migrate_fd_cleanup: accept any negative qemu_fclose() value as error

Also, we now return the qemu_fclose() value unchanged to the caller. For
reference, the migrate_fd_cleanup() callers are the following:

- migrate_fd_completed(): any negative value is considered an
  error, so the change is OK.
- migrate_fd_error(): doesn't check the migrate_fd_cleanup() return value
- migrate_fd_cancel(): doesn't check the migrate_fd_cleanup() return
  value
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

migration.c

@@ -174,9 +174,7 @@ static int migrate_fd_cleanup(MigrationState *s)
 
     if (s->file) {
         DPRINTF("closing file\n");
-        if (qemu_fclose(s->file) != 0) {
-            ret = -1;
-        }
+        ret = qemu_fclose(s->file);
         s->file = NULL;
     } else {
         if (s->mon) {