gk20a_ibus_init_ibus_ring() can be called from gk20a_ibus_intr(), in
non-interruptible context. Replace use of usleep_range() with udelay().
Reported-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NAlexandre Courbot <acourbot@nvidia.com>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>