kselftest/arm64: fp-ptrace: Adjust to new inactive mode behaviour

kselftest/arm64: fp-ptrace: Adjust to new inactive mode behaviour

In order to fix an ABI problem, we recently changed the way that reads
of the NT_ARM_SVE and NT_ARM_SSVE regsets behave when their
corresponding vector state is inactive.

Update the fp-ptrace test for the new behaviour.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Spickett <david.spickett@arm.com>
Cc: Luis Machado <luis.machado@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20250508132644.1395904-25-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>