firmware: arm_scmi: Remove all the unused local variables

While using SCMI iterators helpers a few local automatic variables are
defined but then used only as input for sizeof operators.

cppcheck is fooled to complain about this with:

 | drivers/firmware/arm_scmi/sensors.c:341:48: warning: Variable 'msg' is
 |				not assigned a value. [unassignedVariable]
 |	 struct scmi_msg_sensor_list_update_intervals *msg;

Even though this is an innocuos warning, since the uninitialized variable
is at the end never used in the reported cases, fix these occurences all
over SCMI stack to avoid keeping unneeded objects on the stack.

Link: https://lore.kernel.org/r/20220530115237.277077-1-cristian.marussi@arm.com


Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>