RT1834: Fix PKCS7_verify return value

The function returns 0 or 1, only.
Reviewed-by: NDr. Stephen Henson <steve@openssl.org>

doc/crypto/PKCS7_verify.pod

@@ -91,8 +91,8 @@ timestamp).
 
 =head1 RETURN VALUES
 
-PKCS7_verify() returns 1 for a successful verification and zero or a negative
-value if an error occurs.
+PKCS7_verify() returns one for a successful verification and zero
+if an error occurs.
 
 PKCS7_get0_signers() returns all signers or B<NULL> if an error occurred.