drm/nouveau/bios: make jump conditional

This fixes a hang in VBIOS scripts of the form "condition; jump".
The jump used to always be executed, while now it will only be
executed if the condition is true.

See https://bugs.freedesktop.org/show_bug.cgi?id=72943

Reported-by: Darcy Brás da Silva <dardevelin@cidadecool.com>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: stable@vger.kernel.org