[llvm] [MISched] Fix off-by-one error in debug output with -misched-cutoff=<n> flag (PR #137988)

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

> generally looks good, but could you add a simple test?

put a test up for precommit here #138243 

https://github.com/llvm/llvm-project/pull/137988