rng-egd: offset the point when repeatedly read from the buffer

rng-egd: offset the point when repeatedly read from the buffer

The buffer content might be read out more than once, currently
we just repeatedly read the first data block, buffer offset is
missing.

Cc: qemu-stable@nongnu.org
Signed-off-by: Amos Kong <akong@redhat.com>
Message-id: 1385023371-8198-3-git-send-email-akong@redhat.com
Signed-off-by: Anthony Liguori <aliguori@amazon.com>
(cherry picked from commit 1eb1bd9eafa890f1f4d16ef5cb8b9239a86874d9)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>