ull dereference typo

This is a stray null dereference.  We initialize "ista" properly later on.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
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