staging: erofs: inline erofs_inode_is_data_compressed()

As a helper in erofs_fs.h, erofs_inode_is_data_compressed()
should be inlined.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Link: https://lore.kernel.org/r/20190813023054.73126-1-gaoxiang25@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>