video: console, use DIV_ROUND_UP

Use DIV_ROUND_UP explicitly instead of manual shifts and adds.  It makes
the code more readable and consistent (sometimes there were shifts,
sometimes divs).

There is no change on the assembly level (compilers should do the right
job).

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>