kselftest/arm64: Correct buffer size for SME ZA storage

It looks like a copy-paste error to describe the ZA buffer size using (the
number of P registers * the maximum size of a Z register). This doesn't
have practical impact though as we're always allocating enough space even
for the architectural maximum ZA storage, with SVL equals to 2048 bits.

Switch to use ZA_SIG_REGS_SIZE(SVE_VQ_MAX). setup_za() will need to
initialize two 64MB arraies with this change and can be optimized later (if
someone complain).

Signed-off-by: Zenghui Yu <[e-mail]>
Reviewed-by: Mark Brown <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Catalin Marinas <[e-mail]>

tools/testing/selftests/arm64/abi/syscall-abi.c

···
 	return errors;
 }
 
-uint8_t za_in[SVE_NUM_PREGS * __SVE_ZREG_SIZE(SVE_VQ_MAX)];
-uint8_t za_out[SVE_NUM_PREGS * __SVE_ZREG_SIZE(SVE_VQ_MAX)];
+uint8_t za_in[ZA_SIG_REGS_SIZE(SVE_VQ_MAX)];
+uint8_t za_out[ZA_SIG_REGS_SIZE(SVE_VQ_MAX)];
 
 static void setup_za(struct syscall_cfg *cfg, int sve_vl, int sme_vl,
 		     uint64_t svcr)