Rename PKCS1V15 to PKCS1V15_SIGN

There's PKCS1V15_CRYPT as well (to be added soon).
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index c93da95..3ea87f6 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1211,7 +1211,7 @@
         if( signature_size < rsa->len )
             return( PSA_ERROR_BUFFER_TOO_SMALL );
 #if defined(MBEDTLS_PKCS1_V15)
-        if( PSA_ALG_IS_RSA_PKCS1V15( alg ) )
+        if( PSA_ALG_IS_RSA_PKCS1V15_SIGN( alg ) )
         {
             mbedtls_rsa_set_padding( rsa, MBEDTLS_RSA_PKCS_V15,
                                      MBEDTLS_MD_NONE );