hw/hyperv/hyperv.c: Use device_cold_reset() instead of device_legacy_reset()

hw/hyperv/hyperv.c: Use device_cold_reset() instead of device_legacy_reset()

The semantic difference between the deprecated device_legacy_reset()
function and the newer device_cold_reset() function is that the new
function resets both the device itself and any qbuses it owns,
whereas the legacy function resets just the device itself and nothing
else.  In hyperv_synic_reset() we reset a SynICState, which has no
qbuses, so for this purpose the two functions behave identically and
we can stop using the deprecated one.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-id: 20221013171817.1447562-1-peter.maydell@linaro.org