The producer head pointer in multi producer enqueue fig.6.10
points to incorrect object in the ring array.
Fixes: fc1f2750a3ec ("doc: programmers guide")
Cc: stable@dpdk.org
Signed-off-by: Prateek Agarwal <prateekag@cse.iitb.ac.in>
Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>