video: arm: rpi: Bail out early if querying video information fails

When probing we query for the width and hight of the display. If the
firmware does not report any connected display the system will crash.
See https://github.com/raspberrypi/firmware/issues/1157

 for details.

Signed-off-by: Fabian Vogt <fvogt@suse.com>
[mb: update commit message]
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Andre Przywara <andre.przywara@arm.com>