Gralloc4.0: Correct the default value for unsupported GetChromaSiting

According to Gralloc4.0 VTS definition, ChromaSiting_None is the
expected return value when GetMetadata associated with CHROMA_SITING
is called.

Bug: 154572287
Test: VtsHalGraphicsMapperV4_0

Change-Id: I27bd6f355e1cad8a91a1d9968e3c9d19b1a67768
1 file changed