kselftest/arm64: Enumerate SME rather than SVE vector lengths for za_regs

The za_regs signal test was enumerating the SVE vector lengths rather than
the SME vector lengths through cut'n'paste error when determining what to
test. Enumerate the SME vector lengths instead.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220829160703.874492-2-broonie@kernel.org


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>