fbcon: fix scrolling after logo is cleared

If the 'clear' command is used on the frame buffer with a logo the upper
area is filled by few lines but not scrolled anymore.

Fix this by removing the protected area for the logo if any part of the
logo is cleared.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>