linuxfb plugin will silently fail if unsupported colormap is used

I am developing a device driver for a framebuffer. It is not unusual, not very common but certainly not unusual,  for framebuffers to use RBG888 format. This is a common format the physical camera sensor streams data out in. This data is then read by a Bayer sensor to provide actual RGB888 data that an app uses. The LinuxFB plugin tests for various formats in QImage::Format found in qlinuxfbscreen.cpp.

The 24bit color format should be expanded to include RBG888.

// code plac
const fb_bitfield rbg888[4] = {{16, 8, 0}, {0, 8, 0},
                               {8, 8, 0}, {0, 0, 0}};

In addition QImage::Format should flag an error so a silent failure doesn't go unnoticed.

// code placeholder
if (QImage::Format_Invalid == format)
     qWarning("Unable to determine framebuffer color format.");