macfb: fix black and white modes

macfb won't init in black & white modes since fb_alloc_cmap() no longer
works for zero cmap length. Fix this and also clean up a few printk's and
some stylistic inconsistencies.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>