s3c-fb: only init window colour key controls for windows with blending

The driver clears all windows, but also sets the windows' colour key
controls at the same time.  However, the last window does not have these
registers as it is always blended into the previous window.

Move the colour key initialisation into the probe, and run it for only
nr_win-1 windows.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Pawel Osciak <p.osciak@samsung.com>
Cc: InKi Dae <inki.dae@samsung.com>
Cc: KyungMin Park <kyungmin.park.samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>