library: ssl: adjust return type of mbedtls_psa_alg_from_pk_sigalg()

The correct return type should have been "psa_algorithm_t" since the
beginning because this is what the function really returns and this is
what the returned value is then used for in the calling functions.

Change also the returned value in the default case from
MBEDTLS_PK_SIGALG_NONE to PSA_ALG_NONE in order to return the same type
as in other cases of the switch case.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>

Author: valeriosetti

library/mbedtls_utils.h

@@ -5,8 +5,8 @@
 #define MBEDTLS_UTILS_H
 
 /* Return the PSA algorithm associated to the given combination of "sigalg" and "hash_alg". */
-static inline int mbedtls_psa_alg_from_pk_sigalg(mbedtls_pk_sigalg_t sigalg,
-                                                 psa_algorithm_t hash_alg)
+static inline psa_algorithm_t mbedtls_psa_alg_from_pk_sigalg(mbedtls_pk_sigalg_t sigalg,
+                                                             psa_algorithm_t hash_alg)
 {
     switch (sigalg) {
         case MBEDTLS_PK_SIGALG_RSA_PKCS1V15:
@@ -16,7 +16,7 @@ static inline int mbedtls_psa_alg_from_pk_sigalg(mbedtls_pk_sigalg_t sigalg,
         case MBEDTLS_PK_SIGALG_ECDSA:
             return MBEDTLS_PK_ALG_ECDSA(hash_alg);
         default:
-            return MBEDTLS_PK_SIGALG_NONE;
+            return PSA_ALG_NONE;
     }
 }