HDMI: Reset WakeUpMessageReceived flag when source device asserts <AS>

This patch makes sure the device will send `<Standby>` message when
going to sleep after asserting active source.

Bug: 383849602
Test: atest com.android.server.hdmi
Flag: EXEMPT bugfix
Change-Id: I287f5cf39bc2f285795e16b37274b764453e2482