staging: erofs: clean up initialization of pointer de

Currently pointer de is being initialized with a value that is
never read and a few statements later de is being re-assigned. Clean
this up by ininitialzing de and removing the re-assignment.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>