[llvm] [SLP] More accurately cost RISCV scalar splats (PR #213104)

[via llvm-commits]

gulfemsavrun wrote:

I'm uploading reproducers:
[builds_8670457686257598337_build-debug_clang-crashreports_bus_tests-f5001e.zip](https://github.com/user-attachments/files/32355373/builds_8670457686257598337_build-debug_clang-crashreports_bus_tests-f5001e.zip)
[builds_8670457686257598337_build-debug_clang-crashreports_curve25519-ce81b0.zip](https://github.com/user-attachments/files/32355374/builds_8670457686257598337_build-debug_clang-crashreports_curve25519-ce81b0.zip)


https://github.com/llvm/llvm-project/pull/213104