Modify dimming threshold from 0.2 to 0.9.

We found that the original dimming threshold was relatively
small. When the dimming threshold exceeded 0.2, there were jitter
issues when exiting HDR videos or Ultra HDR photos to the recent
task. For better optimization, we raised the dimming threshold
from 0.2 to 0.9.

Bug: 321864707
Test: Manual

Change-Id: I3dfb987b149b05d4a3c15e14779c9caab4783d75
Signed-off-by: linkai <linkai@xiaomi.com>