hw/net/npcm_gmac: Change error log to trace event

hw/net/npcm_gmac: Change error log to trace event

Convert the LOG_GUEST_ERROR for the "tx descriptor is owned
by software" to a trace message. This condition is normal
when there is there is nothing to transmit, and we would
otherwise spam the logs with it in that situation.

Signed-off-by: Nabih Estefan <nabihestefan@google.com>
Signed-off-by: Roque Arcudia Hernandez <roqueh@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241014184847.1594056-1-roqueh@google.com
[PMM: tweaked commit message]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>