USB: serial: digi_acceleport: remove redundant assignment to pointer priv

Pointer priv is being assigned with a value that is never read, it is
assigned a new value later on in a for-loop. The assignment is
redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Johan Hovold <johan@kernel.org>