drm/lima: simplify the return expression of lima_devfreq_target

Simplify the return expression.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200919100850.1639111-1-liushixin2@huawei.com