sysfs: Use PTR_ERR_OR_ZERO()

Fix ptr_ret.cocci warnings:
fs/sysfs/group.c:409:8-14: WARNING: PTR_ERR_OR_ZERO can be used

Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

Signed-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>