kselftest/arm64: Fix test for streaming FPSIMD write in sve-ptrace

kselftest/arm64: Fix test for streaming FPSIMD write in sve-ptrace

Since f916dd32a943 ("arm64/fpsimd: ptrace: Mandate SVE payload for
streaming-mode state") we do not support writing FPSIMD payload data when
writing NT_ARM_SSVE but the sve-ptrace test has an explicit test for
this being supported which was not updated to reflect the new behaviour.
Fix the test to expect a failure when writing FPSIMD data to the
streaming mode register set.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250609-kselftest-arm64-ssve-fixups-v2-2-998fcfa6f240@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>