bochs_display_setup: return error on failure

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/vgasrc/bochsdisplay.c b/vgasrc/bochsdisplay.c
index e1f90f9..6a75f37 100644
--- a/vgasrc/bochsdisplay.c
+++ b/vgasrc/bochsdisplay.c
@@ -38,7 +38,7 @@
     dprintf(1, "bochs-display: id is 0x%x, %s\n", id
             , id == VBE_DISPI_ID5 ? "good" : "FAIL");
     if (id != VBE_DISPI_ID5)
-        return 0;
+        return -1;
 
      dprintf(1, "bochs-display: using %dx%d, %d bpp (%d stride)\n"
             , FRAMEBUFFER_WIDTH, FRAMEBUFFER_HEIGHT