Fixed output on 16/30 bit screens.
Fixed output on 16/30 bit screens.

Use correct pixman formats for screens which do not use 24 bit
color depth.

Signed-off-by: Tobias Stoeckmann <059b8b880f8441509ec8a65b50b4c6ae74ebea76@stoeckmann.org>

stoeckmann/xwallpaper,stoeckmann/xwallpaper