panfrost: Properly undo pm_runtime_enable when deferring a probe

When deferring the probe because of a missing regulator, we were calling
pm_runtime_disable even if pm_runtime_enable wasn't called.

Move the call to pm_runtime_disable to the right place.

Fixes: 63543079 ("drm/panfrost: Rework runtime PM initialization")
Reported-by: Chen-Yu Tsai <wens@csie.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191023122157.32067-1-tomeu.vizoso@collabora.com