dz: test after postfix decrement fails in dz_console_putchar()

When loops reaches 0 the postfix decrement still subtracts, so the subsequent
test fails.

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Acked-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Johannes Weiner <hannes@saeurebad.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>