Refer to Armv8-A (not Armv8) in docs

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 24b3e03..0dba0a8 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -866,7 +866,7 @@
 #endif
 
 #if defined(MBEDTLS_SHA256_USE_ARMV8_CRYPTO_ONLY) && !defined(MBEDTLS_ARCH_IS_ARMV8)
-#error "MBEDTLS_SHA256_USE_ARMV8_CRYPTO_ONLY defined on non-Armv8 system"
+#error "MBEDTLS_SHA256_USE_ARMV8_CRYPTO_ONLY defined on non-Armv8-A system"
 #endif
 
 /* TLS 1.3 requires separate HKDF parts from PSA,