PM / devfreq: exynos-bus: Fix the wrong return value

This patch fixes the wrong return value. If devfreq driver requires the wrong
and non-available governor, it is fail. So, this patch returns the error
insead of -EPROBE_DEFER.

Fixes: 403e0689 (PM / devfreq: exynos: Add support of bus frequency of sub-blocks using passive governor)
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>