staging: xgifb: delete XGI_OpenCRTC()

Delete redundant function. Also eliminates the following sparse warning:

drivers/staging/xgifb/vb_setmode.c:8033:6: warning: symbol 'XGI_OpenCRTC' was not declared. Should it be static?

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>