fbdev: newport: newport_*wait() return 0 on timeout

With a postfix decrement t reaches -1 on timeout which results in a
return of 0.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
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>