fbdev: fix strerrno since fb->post returns -errno

Signed-off-by: Adrian Negreanu <groleo@gmail.com>
fb.h: add numFramebuffers for JB

Signed-off-by: Adrian Negreanu <groleo@gmail.com>
fbdev: on JB, make use of fb->numFramebuffers

Signed-off-by: Adrian Negreanu <groleo@gmail.com>
Merge pull request #42 from groleo/fbdev-fixes

Fbdev fixes