fchmod/fchmod06.c: cleanup

cleanup of fchmod06.c

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
fchmod/fchmod06.c: add EROFS test for fchmod(2)

add EROFS test in fchmod06.c

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>