kselftest/arm64: Fix check for setting new VLs in sve-ptrace

kselftest/arm64: Fix check for setting new VLs in sve-ptrace

[ Upstream commit 867446f090589626497638f70b10be5e61a0b925 ]

The check that the new vector length we set was the expected one was typoed
to an assignment statement which for some reason the compilers didn't spot,
most likely due to the macros involved.

Fixes: a1d7111257cd ("selftests: arm64: More comprehensively test the SVE ptrace interface")
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Dev Jain <dev.jain@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250609-kselftest-arm64-ssve-fixups-v2-1-998fcfa6f240@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>