Use devm_platform_ioremap_resource() to simplify the code a bit.  This is
detected by coccinelle.

Link: https://lore.kernel.org/r/20190906141727.26552-1-yuehaibing@huawei.comSigned-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>