DecodeGlAccuracyTest: Rename few constants

Few constants used in the test are now marked static and renamed
as per the convention used to name static constants.

Bug: 206034112
Test: atest CtsMediaV2TestCases:DecodeGlAccuracyTest

Change-Id: I06c6e369721e0160181bb1cf5ce5635e6183828a
(cherry picked from commit a84514f10ca88aac38b99e22efe0bf306a383932)
Merged-In: I06c6e369721e0160181bb1cf5ce5635e6183828a
1 file changed