regfiles: Do not serialize remap lookup

We used to have users counter on remap which was
incremented each time this routine was called. Nowadays
remaps are managed w/o the refcounting and we no
longer need global mutex protection for it.

✓ travis-ci: success for Sanitize initialization bits
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/files-reg.c

@@ -623,14 +623,11 @@ struct file_remap *lookup_ghost_remap(u32 dev, u32 ino)
 {
 	struct ghost_file *gf;
 
-	mutex_lock(ghost_file_mutex);
 	list_for_each_entry(gf, &ghost_files, list) {
 		if (gf->ino == ino && (gf->dev == dev)) {
-			mutex_unlock(ghost_file_mutex);
 			return &gf->remap;
 		}
 	}
-	mutex_unlock(ghost_file_mutex);
 
 	return NULL;
 }