[llvm] [RISCV] Correct the limit of RegPresureSet `GPRAll` (PR #118473)

[Luke Lau via llvm-commits]

lukel97 wrote:

[I'm seeing a 2.6% execution time regression on 557.xz_r](https://lnt.lukelau.me/db_default/v4/nts/50?show_delta=yes&show_previous=yes&show_stddev=yes&show_all=yes&show_all_samples=yes&num_comparison_runs=0&test_filter=&test_min_value_filter=&aggregation_fn=min&MW_confidence_lv=0.05&compare_to=51&submit=Update), but I'm not sure if this is accurate. The number of instructions is definitely less and just looking through the code I can see way less spills, so I'm going to rerun it and report back

https://github.com/llvm/llvm-project/pull/118473