doc: erasure-code developer documentation typo

Reported-by: Pavan Rallabhandi <Pavan.Rallabhandi@sandisk.com>
Signed-off-by: Loic Dachary <ldachary@redhat.com>
Merge pull request #2969 from dachary/wip-erasure-code-documentation

doc: erasure-code developer documentation typo

Reviewed-by: Pavan Rallabhandi <Pavan.Rallabhandi@sandisk.com>