crypto: dh - Check mpi_rshift errors

Now that mpi_rshift can return errors, check them.

Fixes: 35d2bf20 ("crypto: dh - calculate Q from P for the full public key verification")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/dh.c

@@ -145,9 +145,9 @@ static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
 	 * ->p is odd, so no need to explicitly subtract one
 	 * from it before shifting to the right.
 	 */
-	mpi_rshift(q, ctx->p, 1);
+	ret = mpi_rshift(q, ctx->p, 1) ?:
+	      mpi_powm(val, y, q, ctx->p);
 
-	ret = mpi_powm(val, y, q, ctx->p);
 	mpi_free(q);
 	if (ret) {
 		mpi_free(val);