gpu/drm: ingenic: Use the plane's src_[x,y] to configure DMA length

Instead of obtaining the width/height of the framebuffer from the CRTC
state, obtain it from the current plane state.

v2: No change

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20191210144142.33143-3-paul@crapouillou.net


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Acked-by: Sam Ravnborg <sam@ravnborg.org>