uprobes: Don't put NULL pointer in uprobe_register()

alloc_uprobe() might return a NULL pointer, put_uprobe() can't deal with
this.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 1666632..336f069 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -897,7 +897,8 @@
 	}
 
 	mutex_unlock(uprobes_hash(inode));
-	put_uprobe(uprobe);
+	if (uprobe)
+		put_uprobe(uprobe);
 
 	return ret;
 }