Below is the call trace of tegra210_init_pllu() function:
  start_kernel()
  -> time_init()
  --> of_clk_init()
  ---> tegra210_clock_init()
  ----> tegra210_pll_init()
  -----> tegra210_init_pllu()

Because the preemption is disabled in the start_kernel before calling
time_init, tegra210_init_pllu is actually in an atomic context while
it includes a readl_relaxed_poll_timeout that might sleep.

So this patch just changes this readl_relaxed_poll_timeout() to its
atomic version.
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Acked-By: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>