[NFC] Remove fractional part of costs in maxbandwidth-regpressure.ll (#187498)
This test is failing on the llvm-clang-x-aarch64 buildbot due to what
looks like a difference in rounding behaviour when printing estimated
cost per lane. Solve this by removing the fractional part, which is what
we've done in the past when this has happened (e.g. commit aeb88f677).