drivers/gpu/drm/i915/dma: style fixes

Fixed several double space pointer notations, and added one newline

Signed-off-by: Robin Schroer <sulamiification@gmail.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>