video/framebuffer: fix bug: jpegview cannot work on framebuffer device other than 16BPP

Force fb_var_screeninfo color format on all Blackfin Framebuffer Drivers.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Cc: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>