Documentation: arm64: Correct SME ZA macros name

It should be ZA_PT_ZA*. ZA_PT_ZA_OFFSET is one example.

It is not ZA_PT_ZA_* because there is one macro ZA_PT_ZAV_OFFSET
that doesn't fit that pattern.

Fixes: 96d32e63 ("arm64/sme: Provide ABI documentation for SME")
Signed-off-by: David Spickett <david.spickett@linaro.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>