px4io: fix array regs[] size (#14135)

may cause memory override if _max_controls larger then _max_actuators

src/drivers/px4io/px4io.cpp

@@ -1306,9 +1306,9 @@ PX4IO::io_set_control_state(unsigned group)
 		controls.control[3] = 1.0f;
 	}
 
-	uint16_t regs[_max_actuators];
+	uint16_t regs[sizeof(controls.control) / sizeof(controls.control[0])] = {};
 
-	for (unsigned i = 0; i < _max_controls; i++) {
+	for (unsigned i = 0; (i < _max_controls) && (i < sizeof(controls.control) / sizeof(controls.control[0])); i++) {
 		/* ensure FLOAT_TO_REG does not produce an integer overflow */
 		const float ctrl = math::constrain(controls.control[i], -1.0f, 1.0f);
 
@@ -1319,12 +1319,12 @@ PX4IO::io_set_control_state(unsigned group)
 			regs[i] = FLOAT_TO_REG(ctrl);
 		}
 
-
 	}
 
 	if (!_test_fmu_fail && !_motor_test.in_test_mode) {
 		/* copy values to registers in IO */
-		return io_reg_set(PX4IO_PAGE_CONTROLS, group * PX4IO_PROTOCOL_MAX_CONTROL_COUNT, regs, _max_controls);
+		return io_reg_set(PX4IO_PAGE_CONTROLS, group * PX4IO_PROTOCOL_MAX_CONTROL_COUNT, regs, math::min(_max_controls,
+				  sizeof(controls.control) / sizeof(controls.control[0])));
 
 	} else {
 		return OK;