simd/archsimd/_gen/simdgen: fix typos in error messages

[jjpinto]

simdgen: fix typos in error messages

[gopherbot]

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[gopherbot]

Message from Keith Randall:

Patch Set 1: Auto-Submit+1 Code-Review+2 Commit-Queue+1

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[gopherbot]

Message from Go LUCI:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2025-12-29T19:08:54Z","revision":"14a9555f0dcff430a942898b50187c7ea303cec2"}

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[gopherbot]

Message from Keith Randall:

Patch Set 1: Code-Review+1

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[gopherbot]

Message from Keith Randall:

Patch Set 1: -Commit-Queue

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[gopherbot]

Message from Go LUCI:

Patch Set 1:

This CL has passed the run

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[gopherbot]

Message from Go LUCI:

Patch Set 1: LUCI-TryBot-Result+1

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