Narrow klass shift should be zero if encoding range extends to 0x1_0000_0000

If we map such that the class space ends at 0x1_0000_0000, we will use shift=3. We should use shift=0.

Repro:

```
thomas@starfish $ ./images/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:CompressedClassSpaceBaseAddress=0xc0000000 -XX:CompressedClassSpaceSize=1g -Xlog:metaspace* -Xshare:off
[0.017s][info][metaspace] Successfully forced class space address to 0x00000000c0000000
[0.017s][info][gc,metaspace] CDS archive(s) not mapped
[0.017s][info][gc,metaspace] Compressed class space mapped at: 0x00000000c0000000-0x0000000100000000, reserved size: 1073741824
[0.017s][info][gc,metaspace] Narrow klass base: 0x0000000000000000, Narrow klass shift: 3, Narrow klass range: 0x100000000
                                                                                                                                                ^^^
```