dmaengine: idxd: remove set but not used variable 'idxd_cdev'

dmaengine: idxd: remove set but not used variable 'idxd_cdev'

drivers/dma/idxd/cdev.c: In function idxd_cdev_open:
drivers/dma/idxd/cdev.c:77:20: warning:
 variable idxd_cdev set but not used [-Wunused-but-set-variable]

commit 42d279f9137a ("dmaengine: idxd: add char driver to
expose submission portal to userland") involed this.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20200210151855.55044-1-yuehaibing@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>