Trival style fix to previous commit to add this detail.

The previous commit also fixed the coordinates passed to the mouse
removal renderer.  The coordinates were rounded down to a character
boundary, and thus essentially unusable.  The renderer had to keep
track of the previous position, or clear a larger area.  The latter
is only safe in the border, which is all that needs special handling
anyway.

I think no renderer depends on the bug.  They have the following
handling:
- gfb sparc64: this seems to assume non-rounded coordinates
- gfb other: does nothing (seems to be missing border handling)
- vga text: does nothing (doesn't need border handling)
- vga planar: clears extras in the border, with some bugs.  The fixes
  will use the precise coordinates to optimize.
- vga direct: clears at the previous position with no check that it
  is active, and clears everything.  Checking finds this bug.
- others: are there any?

sys/dev/syscons/scmouse.c

@@ -252,7 +252,7 @@ sc_remove_mouse_image(scr_stat *scp)
     i = scp->mouse_oldpos;
     mark_for_update(scp, i);
     mark_for_update(scp, i);
-    cols = 1 + howmany(10 - 1, scp->font_width);	/* up to VGA cursor width 9 */
+    cols = 1 + howmany(10 - 1, scp->font_width); /* up to VGA cursor width 9 */
     cols = imax(cols, 2);	/* in case it is text mode 2x2 char cells */
     cols = imin(cols, scp->xsize - i % scp->xsize);
     rows = 1 + howmany(16 - 1, scp->font_size);	/* up to VGA cursor height 16 */