fix(scmi-msg): base: fix protocol list response size

Corrects the size of the SCMI response payload when querying the list
of the supported protocol. This response payload size depends on the
number of protocols enumerated by the response.

Change-Id: Ib01eb5cec6c6656dfd7d88ccdd5a720c1deee7a3
Reported-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>