gpu: host1x: Check INCR opcode correctly

The firewall code used a wrong loop condition (pointer to a
structure) while checking INCR opcode. This patch fixes the code to
use correct loop condition (number of words remaining).

Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>