We already have a cifs_set_file_info function that can flip DOS
attribute bits. Have cifs_unlink call it to handle turning ATTR_HIDDEN
on and ATTR_READONLY off when an unlink attempt returns -EACCES.

This also removes a level of indentation from cifs_unlink.
Signed-off-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NSteve French <sfrench@us.ibm.com>