dt-bindings: firmware: arm,scmi: Add missing vendor string

Recently introduced max-rx-timeout-ms optionao property is missing a
vendor prefix.

Add the vendor prefix so that it aligns with the new properties that
are about to get added soon.

Fixes: 3a5e6ab0 ("dt-bindings: firmware: arm,scmi: Introduce property max-rx-timeout-ms")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Message-Id: <20241028120151.1301177-7-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>