PackageDexOptimizer: fix typo in log message.

'oatDir' is the only token that has a space around the '='. None of the
other tokens in the log message do. Make the log message consistent so
that grepping is easier -- and the log message looks better.

Before:
PackageManager.DexOptimizer: Running dexopt (dex2oat) on:
/system/priv-app/Telecom/Telecom.apk pkg=com.android.server.telecom
isa=arm64 vmSafeMode=false debuggable=false
target-filter=interpret-only oatDir = null sharedLibraries=null

After:
PackageManager.DexOptimizer: Running dexopt (dex2oat) on:
/system/priv-app/Telecom/Telecom.apk pkg=com.android.server.telecom
isa=arm64 vmSafeMode=false debuggable=false
target-filter=interpret-only oatDir=null sharedLibraries=null

Bug: None
Test: Build, flash, grep for log message.
Change-Id: I84162ec3535e3f83a60a62d40cbaf8e74d2051c6