davinci: cpufreq: bailout on regulator errors

Current cpufreq code does not consider errors that can occur while
changing voltage. Code to increase CPU  frequency goes ahead even in
the case the regulator has failed to increase the voltage. This leads
to hard error since lower voltages cannot support increased frequency.

Prevent this by not increasing frequency in case increasing voltage
is not successful.

Also, do not lower the voltage if changing the cpu frequency has failed
for some reason.

Note that we do not return error on failure to decrease voltage as
that is not a hard error.

Build fix for non-cpufreq kernels by Caglar Akyuz.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Cc: Caglar Akyuz <caglar@bilkon-kontrol.com.tr>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>