Tegra: Fix the delay loop used during SC7 exit

Tegra: Fix the delay loop used during SC7 exit

This patch fixes the delay loop used to wake up the BPMP during SC7 exit.
The earlier loop would fail just when the timer was about to wrap-around
(e.g. when TEGRA_TMRUS_BASE is 0xfffffffe, the target value becomes 0,
which would cause the loop to exit before it's expiry).

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>