[PATCH] dma/idxd: fix missing default for workqueue options

[Walsh, Conor]

> When no --wq-option flag is passed to dpdk_idxd_cfg.py script, the
> default value used by argparse is None. This leads to later errors which
> are expecting an array value:
> 
> 	TypeError: 'NoneType' object is not iterable
> 
> This is fixed by specifying that the empty array should be the default
> if no flags are passed.
> 
> Fixes: 94b0f04dc0e3 ("dma/idxd: add generic option for queue config")
> 
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> ---

Acked-by: Conor Walsh <conor.walsh at intel.com>