Fix erroneous macro guards

Replace MBEDTLS_SHA256_C for PSA_WANT_ALG_SHA_256
everywhere, including comments and print statements.

Signed-off-by: Thomas Daubney <thomas.daubney@arm.com>
diff --git a/programs/psa/psa_hash.c b/programs/psa/psa_hash.c
index 47ba2dc..9cd5a3e 100644
--- a/programs/psa/psa_hash.c
+++ b/programs/psa/psa_hash.c
@@ -49,7 +49,7 @@
 #if !defined(MBEDTLS_PSA_CRYPTO_C) || !defined(PSA_WANT_ALG_SHA_256)
 int main(void)
 {
-    mbedtls_printf("MBEDTLS_PSA_CRYPTO_C and MBEDTLS_SHA256_C"
+    mbedtls_printf("MBEDTLS_PSA_CRYPTO_C and PSA_WANT_ALG_SHA_256"
                    "not defined.\r\n");
     return EXIT_SUCCESS;
 }
@@ -160,4 +160,4 @@
     mbedtls_psa_crypto_free();
     return EXIT_SUCCESS;
 }
-#endif /* MBEDTLS_PSA_CRYPTO_C && MBEDTLS_SHA256_C */
+#endif /* MBEDTLS_PSA_CRYPTO_C && PSA_WANT_ALG_SHA_256 */