staging: erofs: refine erofs_allocpage() remove duplicated code in decompressor by introducing failable erofs_allocpage(). Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com> Link: https://lore.kernel.org/r/20190731155752.210602-14-gaoxiang25@huawei.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>