drivers/video/fbdev/sis/sis_main.c: remove unnecessary test on unsigned value

unsigned value is never < 0

Cc: Jean-Christophe Plagniol-Villard <[e-mail]>
Cc: Tomi Valkeinen <[e-mail]>
Signed-off-by: Fabian Frederick <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/fbdev/sis/sis_main.c

···
 	/* Adapt RGB settings */
 	sisfb_bpp_to_var(ivideo, var);
 
-	/* Sanity check for offsets */
-	if(var->xoffset < 0) var->xoffset = 0;
-	if(var->yoffset < 0) var->yoffset = 0;
-
 	if(var->xres > var->xres_virtual)
 		var->xres_virtual = var->xres;