Replace MBEDTLS_MD_CAN_SHA256 with PSA_WANT_ALG_SHA_256

Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
index be55963..cba513d 100644
--- a/library/ssl_cookie.c
+++ b/library/ssl_cookie.c
@@ -40,7 +40,7 @@
  * If DTLS is in use, then at least one of SHA-256 or SHA-384 is
  * available. Try SHA-256 first as 384 wastes resources
  */
-#if defined(MBEDTLS_MD_CAN_SHA256)
+#if defined(PSA_WANT_ALG_SHA_256)
 #define COOKIE_MD           MBEDTLS_MD_SHA256
 #define COOKIE_MD_OUTLEN    32
 #define COOKIE_HMAC_LEN     28