riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

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                    "vendor": "Linux",
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                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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                        "arch/riscv/net/bpf_jit_comp64.c"
                    ],
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