[llvm] [RISCV] Ignore debug instructions in epilogue block checks (PR #219401)

[Yongqiang Tian via llvm-commits]

yqtian-se wrote:

Thanks for the review! I addressed all three comments in [892151c3b](https://github.com/llvm/llvm-project/pull/219401/commits/892151c3b4324ac05d912f231071adcc958c1631). Pls let me know if anything else should be changed. Thx!

https://github.com/llvm/llvm-project/pull/219401