vx800/vga.c: Remove extraneous parentheses.

Change-Id: Ic81b5f66871ec78c72f2adc5723f22fa94a672e8
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/7682
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)