8346954: [JMH] jdk.incubator.vector.MaskedLogicOpts fails due to IndexOutOfBoundsException
Suite MaskedLogicOpts.maskedLogicOperationsLong512() failed on both x86
and AArch64 with the following error:
```
java.lang.IndexOutOfBoundsException: Index 252 out of bounds for length 249
```
The variable `long256_arr_idx` is misused when indexing 'LongVector
l2, l3, l4, l5' in function `maskedLogicOperationsLongKernel()`.
'long256_arr_idx' increases by 4 every time the benchmark runs and
ensures the incremented value remains within the bounds of the array.
However, for `LongVector.SPECIES_512`, it loads 8 numbers from the
array each time the benchmark runs, resulting in an out-of-range
indexing issue.
Hence, we revised the index variables from `long256_arr_idx` to
`long512_arr_idx`, which has a stride of 8, to ensure that the loaded
vector is inside of the array boundary for all vector species. This is
also consistent with other kernel functions.
Additionally, some defined but unused variables have been removed.
Change-Id: I8a728e6d3c2b54353559294d62cec7005b6552d5