media: platform: exynos4-is: fix return value check in fimc_md_probe()

devm_pinctrl_get() may return ERR_PTR(-EPROBE_DEFER), add a minus sign
to fix it.

Fixes: 4163851f ("[media] s5p-fimc: Use pinctrl API for camera ports configuration")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>