vgabios: Limit the range of the VBE number of "pages" parameter.

Looking at the output of other VGA BIOS implementations, it appears
that the number of available video pages reported is always between 1
and 127.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/vgasrc/vbe.c b/vgasrc/vbe.c
index d962333..2c08736 100644
--- a/vgasrc/vbe.c
+++ b/vgasrc/vbe.c
@@ -144,6 +144,10 @@
             mode_attr |= VBE_MODE_ATTRIBUTE_LINEAR_FRAME_BUFFER_MODE;
         break;
     }
+    if (pages > 128)
+        pages = 128;
+    if (pages < 2)
+        pages++;
     SET_FARVAR(seg, info->mode_attributes, mode_attr);
     SET_FARVAR(seg, info->planes, planes);
     SET_FARVAR(seg, info->pages, pages - 1);