Simplify the exit conditions for dumpstate

Now that the exit conditions are mostly in one place it is more readable
to directly call exit.

BUG:111441001
Test: /system/bin/dumpstate -d || echo "bad flag works as expected"
Test: /system/bin/dumpstate -h && echo "help flag works as expected"
Test: adb bugreport a.zip
Change-Id: Ie40d81a3317ad8bb97c825523533ea3fa1016733