fs: return EOPNOTSUPP from file_setattr/file_getattr syscalls

These syscalls call to vfs_fileattr_get/set functions which return
ENOIOCTLCMD if filesystem doesn't support setting file attribute on an
inode. For syscalls EOPNOTSUPP would be more appropriate return error.

Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>