dt-bindings: irqchip: ti, sci-inta: Fix diagram indentation for unmapped events

One space has been missing by the diagram update.

Fixes: bb2bd7c7f3 ("dt-bindings: irqchip: ti, sci-inta: Update for unmapped event handling")
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201103135004.2363-1-peter.ujfalusi@ti.com

Documentation/devicetree/bindings/interrupt-controller/ti,sci-inta.yaml

@@ -34,7 +34,7 @@ description: |
                        |                                         |
                        |      Unmap                              |
                        | +--------------+                        |
- Unmapped events ----->| |   umapidx    |-------------------------> Globalevents
+  Unmapped events ---->| |   umapidx    |-------------------------> Globalevents
                        | +--------------+                        |
                        |                                         |
                        +-----------------------------------------+