Replace `MBEDTLS_MD_CAN_SHA512` with `PSA_WANT_ALG_SHA_512`

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/programs/ssl/ssl_test_lib.c b/programs/ssl/ssl_test_lib.c
index 2419bba..2aa2d88 100644
--- a/programs/ssl/ssl_test_lib.c
+++ b/programs/ssl/ssl_test_lib.c
@@ -115,7 +115,7 @@
 #elif defined(MBEDTLS_HMAC_DRBG_C)
 #if defined(PSA_WANT_ALG_SHA_256)
     const mbedtls_md_type_t md_type = MBEDTLS_MD_SHA256;
-#elif defined(MBEDTLS_MD_CAN_SHA512)
+#elif defined(PSA_WANT_ALG_SHA_512)
     const mbedtls_md_type_t md_type = MBEDTLS_MD_SHA512;
 #else
 #error "No message digest available for HMAC_DRBG"