arm64/sme: Fix __finalise_el2 SMEver check

When checking for ID_AA64SMFR0_EL1.SMEver, __check_override assumes
that the ID_AA64SMFR0_EL1 value is in x1, and the intent of the code
is to reuse value read a few lines above.

However, as the comment says at the beginning of the macro, x1 will
be clobbered, and the checks always fails.

The easiest fix is just to reload the id register before checking it.

Fixes: f122576f ("arm64/sme: Enable host kernel to access ZT0")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>