uavcan: use timer 6 by default on stm32f7

src/drivers/uavcan/CMakeLists.txt

@@ -51,7 +51,7 @@ if(CONFIG_ARCH_CHIP)
 		endif()
 	elseif(${CONFIG_ARCH_CHIP} MATCHES "stm32")
 		set(UAVCAN_DRIVER "stm32")
-		set(UAVCAN_TIMER 5) # The default timer is TIM5
+		set(UAVCAN_TIMER 6) # The default timer is TIM6
 		if (DEFINED config_uavcan_timer_override)
 			set (UAVCAN_TIMER  ${config_uavcan_timer_override})
 		endif()