cpufreq: tegra186: Simplify probe return path

We always put the reference to BPMP device on exit of the Tegra186
CPUFREQ driver and so there is no need to have separate exit paths
for success and failure. Therefore, simplify the probe return path
in the Tegra186 CPUFREQ driver by combining the success and failure
paths.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>