virtio-msg: fix Bus Specific Messages label path

Update the label path for "Bus Specific Messages" to match the Bus
Messages section hierarchy, keeping labels consistent with the document
structure.

Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>

Author: bertrand-marquis

transport-msg.tex

@@ -1565,7 +1565,7 @@ \subsubsection{Overview}
 \end{tabular}
 
 \paragraph{Bus Specific Messages}
-\label{sec:Virtio Transport Options / Virtio Over Messages / Bus Operation / Bus Specific Messages}
+\label{sec:Virtio Transport Options / Virtio Over Messages / Bus Messages / Bus Specific Messages}
 
 A range of message IDs are reserved for use by the specific bus
 implementation. These messages can be used for any implementation specific