ImageReaderDecoderTest: Fix swirl validation for 10-bit cases

All the computations in swirl validations are based on 8-bit data.
So after decoding 10-bit clips, instead of generating statistics
using 10-bit data, use 8 most significant bits so that all the
calculations in the tests can continue with 8-bit precision.

Bug: 214634656
Test: atest CtsMediaDecoderTestCases:ImageReaderDecoderTest
Change-Id: I3f3e1984aa21596ff8c5187cc725a63dc7fbd2e9
2 files changed