migration: remove unreachable code after reading data

The code calls qio_channel_read() in a loop when it reports
QIO_CHANNEL_ERR_BLOCK. This code is reported when errno==EAGAIN.

As such the later block of code will always hit the 'errno != EAGAIN'
condition, making the final 'else' unreachable.

Fixes: Coverity CID 1490203
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220627135318.156121-1-berrange@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/qemu-file.c

@@ -411,10 +411,8 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
         f->total_transferred += len;
     } else if (len == 0) {
         qemu_file_set_error_obj(f, -EIO, local_error);
-    } else if (len != -EAGAIN) {
-        qemu_file_set_error_obj(f, len, local_error);
     } else {
-        error_free(local_error);
+        qemu_file_set_error_obj(f, len, local_error);
     }
 
     return len;