fbcon: don't draw cursor when it's disabled

When the cursor and echo are disabled on the current console, pressing a
key will cause a black rectangle to be painted in the cursor's position.
Fix this by not touching the framebuffer in fbcon_cursor() when the
cursor is off.

Signed-off-by: Michal Januszewski <spock@gentoo.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>