PM / devfreq: Fix incorrect usage of IS_ERR_OR_NULL in exynos5_bus.c

platform_device_register_simple does not return NULL.
Hence NULL check is not required.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>