hw/intc/arm_gicv3_its: Fix handling of process_its_cmd() return value

hw/intc/arm_gicv3_its: Fix handling of process_its_cmd() return value

process_its_cmd() returns a bool, like all the other process_ functions.
However we were putting its return value into 'res', not 'result',
which meant we would ignore it when deciding whether to continue
or stall the command queue. Fix the typo.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20220111171048.3545974-4-peter.maydell@linaro.org