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

One space has been missing by the diagram update.

Fixes: bb2bd7c7f3d0 ("dt-bindings: irqchip: ti, sci-inta: Update for unmapped event handling")
Reported-by: Rob Herring <[e-mail]>
Signed-off-by: Peter Ujfalusi <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

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

···
                        |                                         |
                        |      Unmap                              |
                        | +--------------+                        |
- Unmapped events ----->| |   umapidx    |-------------------------> Globalevents
+  Unmapped events ---->| |   umapidx    |-------------------------> Globalevents
                        | +--------------+                        |
                        |                                         |
                        +-----------------------------------------+