drm/nvc0-/gr: shift wrapping bug in nvc0_grctx_generate_r406800

We care about the upper 32 bits here so we have to use 1ULL instead of 1
to avoid a shift wrapping bug.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>