Instead of looking at plane->fb let's look at the proper new
plane state.

Not that the code makes a ton of sense. It's only going through the
crtcs in the atomic state, so assuming not all of them are included
we're not even calculating the total bandwidth here. Also we're
not considering whether each crtc is actually enabled or not.

Cc: Deepak Rawat <drawat@vmware.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Sinclair Yeh <syeh@vmware.com>
Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525185045.29689-2-ville.syrjala@linux.intel.comReviewed-by: Sinclair Yeh <syeh@vmware.com>