OomAdjuster: Don't reset raw adj if it has been evaluated

Fix an issue that sometimes the adj of the connected process
couldn't be evaluated correctly.

Bug: 145589327
Test: atest MockingOomAdjusterTests
Test: atest CtsAppTestCases:ActivityManagerProcessStateTest
Change-Id: Icc4f1f444b2b94d65787e8b5c94ab4830c8dbb48