Fixes gcc '-Wunused-but-set-variable' warning:

drivers/fpga/dfl-fme-main.c: In function ‘fme_dev_destroy’:
drivers/fpga/dfl-fme-main.c:678:18: warning: variable ‘fme’ set but not
used [-Wunused-but-set-variable]

It is never used and so can be removed.
Acked-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>