hw/arm/iotkit: Fix IRQ number for timer1

A cut-and-paste error meant we were incorrectly wiring up the timer1
IRQ to IRQ3. IRQ3 is the interrupt for timer0 -- move timer0 to
IRQ4 where it belongs.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180727113854.20283-3-peter.maydell@linaro.org