Revert "staging: erofs: disable compiling temporarile"

This reverts commit 156c3df8.

Since XArray and the new mount apis aren't merged in 4.19-rc1
merge window, the BROKEN mark can be reverted directly without
any problems.

Fixes: 156c3df8 ("staging: erofs: disable compiling temporarile")
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>