video: fbdev: intelfb: Initialize value of stolen size

Variable stolen_size can be left uninitialized in a code path with
INTEL_855_GMCH_GMS_DISABLED. Fix this by initializing the variable to 0.

Also fix indentation of function arguments.

Signed-off-by: Petr Cvek <petrcvekcz@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>