mandelbrot: use correct colors on greyscale targets (FS#10935)
Tested on Clipv1 (sim/target) and Ipod3g (sim)
Each color would be calculated as 0
Note the iteration over the whole range of colors is quite weird, and I
can not really sense what max_iter represents (except it's a number of
different colors, right?)
It should be backported to branch after tomers check if color range is
correct (FS#10935 mentions much smaller range for color targets as well)
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@24377 a1c6a512-1295-4272-9138-f99709370657