Fix the following coccicheck warning:

drivers/uio/uio_dmem_genirq.c:47:5-8: Unneeded variable: "ret". Return
"0" on line 71
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200428063155.42349-1-yanaijie@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>