clk: tegra30: Don't wait for PLL_U lock bit

The lock bit on PLL_U does not seem to be working correctly and
sometimes never gets set when waiting for the PLL to come up.
Remove the TEGRA_PLL_USE_LOCK flag to use a constant delay.

Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>