sim: Simplify collecting the key value in initParam.

sim: Simplify collecting the key value in initParam.

If the first register is all zeroes, it doesn't really matter what the
other register is. If the first register has the entire string, we still
don't care what the other register has in it. There's no reason to
complicate the code with these extra checks.

Change-Id: I22ad521b9ace915ccb75f15934fc6b3d650d5293
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27228
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>