Start HOME activity only if we are not on it yet

HDMI framework does not know if the current device is on Youtube or
Netflix when the current device is the current Active Source. When related
cec messages received by the current device that could refresh its
Active Source status, we should not start HOME activity since it might
not be on the HOME activity right now.

Test: manual
Bug: 131601411
Change-Id: I9de3267139c2fb4a8ad55f50196dfea15a1097d8
(cherry picked from commit 596efe9c799ce5b9d92b92867d7250fbf2eb1490)