Replace MBEDTLS_MD_CAN_SHA256 with PSA_WANT_ALG_SHA_256

Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/library/x509.c b/library/x509.c
index 3560490..199c4fb 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -141,7 +141,7 @@
         case MBEDTLS_MD_SHA224:
             return "SHA224";
 #endif
-#if defined(MBEDTLS_MD_CAN_SHA256)
+#if defined(PSA_WANT_ALG_SHA_256)
         case MBEDTLS_MD_SHA256:
             return "SHA256";
 #endif