[llvm-mca][BtVer2] Modify ANDN tests in zero-idioms-avx-256.s. NFC
[llvm-mca][BtVer2] Modify ANDN tests in zero-idioms-avx-256.s. NFC

Two test cases should have tested 256-bit variants of VANDN zero-idioms instead
of the 128-bit variants.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@342655 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm