Use MBEDTLS_MD_LIGHT instead of MBEDTLS_MD_C

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 2b6c8d4..959b945 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -261,7 +261,7 @@
             return PSA_ERROR_INSUFFICIENT_ENTROPY;
 #endif
 
-#if defined(MBEDTLS_MD_C)
+#if defined(MBEDTLS_MD_LIGHT)
         case MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE:
             return PSA_ERROR_NOT_SUPPORTED;
         case MBEDTLS_ERR_MD_BAD_INPUT_DATA: