library: add remaining changes for the new ECP_LIGHT symbol

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 9cccf53..ec12a3f 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -378,7 +378,7 @@
 /* Key management */
 /****************************************************************/
 
-#if defined(MBEDTLS_ECP_C)
+#if defined(MBEDTLS_ECP_LIGHT)
 mbedtls_ecp_group_id mbedtls_ecc_group_of_psa(psa_ecc_family_t curve,
                                               size_t bits,
                                               int bits_is_sloppy)
@@ -470,7 +470,7 @@
     (void) bits_is_sloppy;
     return MBEDTLS_ECP_DP_NONE;
 }
-#endif /* defined(MBEDTLS_ECP_C) */
+#endif /* MBEDTLS_ECP_LIGHT */
 
 psa_status_t psa_validate_unstructured_key_bit_size(psa_key_type_t type,
                                                     size_t bits)