As the allocation and free buffer that need to add mutex lock for drm mm,
but it lacks the locking on error path in rockchip_gem_iommu_map().
Also, the trivial changes like The comment should be  placed in the
kerneldoc and unused blank line.
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Reviewed-by: Mark Yao <mark.yao@rock-chips.com>
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1496196863-25738-1-git-send-email-wxt@rock-chips.com