arm/tegra: clk_get should not be fatal

The timer and rtc-timer clocks aren't gated by default, so there is no reason
to crash the system if the dummy enable call failed.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>