cxgb4: Convert to use simple_open()

Remove an open coded simple_open() function and replace file
operations references to the function with simple_open()
instead.

Generated by: scripts/coccinelle/api/simple_open.cocci

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>