skeletonfb: update to correct platform driver usage

It updates skeletonfb to new platform driver API.  The skeletonfb is
templates for creating new drivers.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>