misc: vexpress: Use PTR_ERR_OR_ZERO()

Fix ptr_ret.cocci warnings:
drivers/misc/vexpress-syscfg.c:273:1-3: 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>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>